Howzit James
Firstly, welcome to the Big A!
Regarding your query... 
Bit of a bummer that Aero and Bax don't reply to your mails... I'm not sure if Aero are even still producing commercial model kits... Bax mod are still producing, I'm not sure why Chris hasn't replied to your mail, when I mail him I get a reply within a few hours... When did you mail him? As he has been overseas recently and perhaps hasn't noticed the mail... 
Baxmod produce many of the SADF and SANDF vehicles in 1/72 resin, and they are regulars on the IPMS Cape Town competition night. Chris is working on a 1/35 SANDF vehicle, but the vehicle name slips my mind at the moment. As I said, keep mailing Chris, I'm confident he will reply when he gets a chance.
The Olifant MkIB resin conversion kit Michael refers to was for the Tamiya 1/35 Centurion. The Centurion, until recently, was OOP. And thus when the moulds for the conversion kit tired, the designer and the manufacturer parted ways and retired the moulds and the operation. That said, Tamiya has recently reintroduced their Centurion, so perhaps if their is enough demand we will see the kit re-released. Added to that Government's decision to re-introduce the Olifant upgrade programme.... who knows.... maybe we'll see someone produce a MkII upgrade kit soon...
As for the lack of SANDF armour.... well strickly speaking the only armour we have is the Olifant... the rest is categorised as soft-skins... but either way... it's simple economics... supply and demand.... there is simply not enough demand to justify ANY of the big boys mass producing SANDF vehicles. Hell, if they're not even prepared to produce WWII Allied vehicles and figures, which I'll guarantee you has a bigger potential market than SANDF vehicles, what chance do you really think there is of them producing the SANDF stuff?? Remember, these guys deal with the global market. They don't think about the 200 odd serious modellers in one little country in southern Africa... 
Think about it... if you had the opportunity to produce one of two products... the first one, you could potentially sell 200,000 units at $50... the second, you could sell maybe 1,000 units at $60.... which would you choose?
As for our armour being rated as among the best in the world? A MBT designed in 1944/5? And upgraded with parts no-one else wanted? No. There are far better MBT's than the Olifant. 
Yes, our IED equipment is definitely amongst the best. There is no doubt about that. Heck, we can't sell the Rooivalk, but we sure sold a lot of IED vehicles... 
 Time to get off the soapbox... but please feel free to debate any of my points...  

  :-)  
 Rudi