There is NOTHING written into law that states S/A passport holders must go back to their country to get a Non-B visa (or any visa). There are S/A's who have visas from Pretoria that have writing on them stating they need to go back to S/A to get a visa and at this time Vientiane is NOT letting people get any visa if you have that writing on a visa from Pretoria.
K/L has a new policy that S/A passport holders have to have their applications approved by the MFA in thailand before they will issue visas to them (and as
@Ron ******
said it is taking 4 weeks for that). Penang wil issue Non-B's for teaching but anyone applying there needs police checks from both their country AND thailand.
Vientiane will issue them without a problem (as long as you don't have a visa from Pretoria with thai writing on it) and you only need a police background check from either your country OR thailand.