As far as I know, there are different importers (wholesale?) from different producers?

The local gun shops order from different suppliers.

Sometimes, the suppliers order together to save on transportation costs.

As far as I know, there are different importers (wholesale?) from different producers?

YES but how many ?
I suggest perhaps three or four - dominate the complete firearms - reloading - import supply chain .. !

I think Nyati (linked to Safari Gunshops) is another importer. The links between these companies might make the total smaller.

Importers of Firearms in South Africa
In South Africa, the import of firearms is regulated under the South African Firearms Control Act, 2000. Here are some key players in the firearms import and distribution industry:
Nicholas Yale: A leading firearm importer and distributor in Southern Africa, offering a wide range of tactical rifles, pistols, revolvers, shotguns, sights, ammo, and firearm parts.
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Luckys Sport: A trusted firearm importer and distributor, specializing in importing and wholesaling firearms and accessories from top global manufacturers.
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SAAADA: The South African Arms and Ammunition Dealers’ Association, representing firearms dealers, importers, manufactures, gunsmiths, and related trades.
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Kalahari Arms: A family-run concierge gun shop offering personalized training, range time, and in-house gunsmithing services.
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These companies play a crucial role in the firearms trade in South Africa, ensuring compliance with the law and providing a range of services to meet the needs of their clients.

Its worrying that there are so few players, not many pins to topple if there is a fight.

From regular contact with gun shop owners I have learned a few things which makes the situation  understandable, whether we like it or not:

- the firearm franchise is a fairly small business in SA
- the paperwork is vast

This means that few folks are capable and willing to go the extra mile(s) to get all the things done before any form of restricted item (primer, powder, cartridge or firearm) lands on the shelf for sale. That is also why the wholesalers work together. 

Further to Ds J's points above, we're a tiny market with a generally business unfriendly legal and regulatory environment which is also fiercely obstructive to the trade in anything firearm related.

On top of that we have a 'foreign policy' that makes western countries increasingly reluctant to send us anything firearm related. Any business that operates in such an environment could put their investment in much safer places and their margins and number of competitors reflect that.

I suspect much worse is to come and these will be looked back on as part of the golden years.

When it comes to reloading components, there is only one big one; Normark. They import Berger and Lapua.

Years ago Nicholas Yale imported Lapua bullets and brass directly from Lapua. The prices were reasonable. As the price of Berger bullets increased, Lapua, with their better BC, similar QC and cheaper price started to draw more users. I am quite sure Normark was not happy about that.

When the old man died, Normark took over importing and the prices increased drastically.

The fuckers even went so far to contact Lapua to be the sole importer into SA. So now Lapua wont even sell to any other entrepreneur that want to import to South Africa.

Sierra is being imported by African Hunting Supplies.

So far the prices for Hornady bullets are not too bad, but I expect Normark to worm their way into that as well next time Nocholas Yale has a hiccup.

The fuckers even went so far to contact Lapua to be the sole importer into SA. So now Lapua wont even sell to any other entrepreneur that want to import to South Africa.

THIS ..
SOLE supplier and importer = closed shop - make the price anything you want !

What puts the breaks on these guys going too wild on bullet prices is the fact that local production has the promise of biting into the market. A bullet is "relatively" easy to make. You either need swaging dies or a CNC lathe for monos and you can enter the market. Other components like primers or propellants take big investment.

You can also see what margins they make by looking at US prices. Take a US price, and add shipping and import duty and compare that to what it costs locally. If we compare retail prices of say a Hornady Interlock here and in the USA, I would expect the local price to be about 50% more. If it is more than 50%, someone is getting greedy. e.g. in the US a 150gr .30 Interlock goes for $38/100 = R700. The same things here retails between R1000-R1200 which is reasonable.

A bullet is easy to make. The jacket, not so much. What makes Bergers so good is the J4 jackets that have exceptional thickness consistancy. So too the lead QC with regards to homogeneity and lack of inclusions.

Sierra is almost as good, but i think they feed the output from multiple machines into a single batch, leading to intra-batch variation in shape.

Hornady, not so much, but their marketing is great. They have a massive range with a few prduct that have good consistancy. Their relatively new jackets are doing much better than their legacy lines.

Wher PMP went wrong was lack of maintenence and replacement of their swaging dies. They just ran what they had until the wear put them out of spec. Not having a replacement schedule made that they could not continue with commercial bullet production. So they focussed on their bread-and-butter military bullets. Probably using dies imported at great cost. Also did not help that their QC was not on par...

Is brown box PMP cartridges still available?