There are HK collapsible stocks with a mechanical buffer designed for the HK93. However they are harder to find and typically more expensive. If you watch the for sale section here and check gun broker you should be able to find a used one eventually. Note : There are some collapsible stocks made for HK93s that have buffered bolt carriers. These stocks are the proper length but have only the H buffer and no mechanical buffer. So before you buy a stock make sure that it is a mechanically buffered stock.
The diagram at hk parts clearly shows the mechanical buffer.
There are a couple other ways to get a properly buffered collapsible stock for a HK93. Probably the cheapest and easiest would be to buy a G3 collapsible stock and cut down the end cap on the stock from a double pin to a single pin. The rails would be too long so the stock would not fully close.
Another option would be to buy and assemble an end cap with the proper buffer for a HK 93 collapsable stock. I think RTG has all of the parts to do this. you could then combine this with the rails and butt pad from either a G3 collapsible stock (the rails would be too long to close) or with one from an MP5 collapsible stock like the ATI (the rails on the MP5 stocks are shorter than HK93 stocks).
I am not very familiar with the internal differences between the HK93 and the Z43. However, I believe there is an internal block of some sort in the Z43 that would prevent the use of a standard full-auto Hk33 bolt carrier. I don't know if it would be practical (or more importantly legal) but it may be possible to have a HK33 Buffered bolt carrier from a Malaysian HK33 machined to function properly in your Z43. If so you could use an MP5 collapsible stock.