Can hardly believe it, but I got none left - even dug out an old 286 board...
There's plenty on ebay, prices are a bit like a rip off but you'll probably be able to fetch a set for $10 or below. Just look out for 4164, 4264, 5164, any 64k DRAM.
While you're at it - check voltage out of the PSU: if 5V is below ~4.8V you'll get RAM problems, too. In that case you need to cut it open and replace the (poorly cooled) 7805. There's another 7805 on the board, but I've never had that one die.
