Sorry for the delay getting this info for you. It slipped my mind for a bit - been studying too hard! :-)
Each of the four RAM chips I plugged in to my CV64 are branded "Silicon Magic" and have a speed of "66MHz". They are numbered "C9728 SM81C256K16BJ -35". I'm not sure whether the "C9728" and "-35" bits are part of it as they are somewhat separated from the long string of characters. To possibly save you some legwork, I was unable to find any of the chips for sale separately, except for from one retailer who would only sell them in large quantities. It was much cheaper in the end to get two 1MB S3 Virge Trio cards from eBay. They have four chips on each, two of which are surface mounted and two of which are socketed (which is why you need two cards to get the full set of four chips for the CV).
HTH
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moto