I beleive some of the early S3 PCI graphics cards used these chips, had 2 soldered on the board for 2meg, and sockets for another 2meg.. check with local computer shops for old stock, garage sales or computer swap meets. Look at the cards, if they have 4meg, with 2 in sockets, check the memory in those sockets are the same as what you need.
Buy the card cheap, rip out the memory and upgrade your Cybervision64 :-)
Az