There is a small demand for this product. Enough to boost the prices for individual sales on ebay. The demand is from people who do not have an accelerator which takes RAM and people for which 146Mbytes is not enough.
This is just a handful of Amiga users. Certainly not enough to produce a product at a sensible price with profit which would cover the R&D and initial product run.
Most people just wait till they have a bit more money and then buy an accelerator with a RAM interface.
The cost differential between a new Zorro RAM card and a second hand Apollo 4040 is almost non.
Separate the Amiga users who have a Zorro III capable Amiga, then separate out those who do not have an accelerator with RAM, then separate out those who want more RAM, it's not that many.