Just posted this on the Trading Post forum, but thought I'd include it here, too:

I found a pretty good deal on eBay for 128MB SIMMs that I have confirmed are compatible (and small enough to fit properly) in the LC 475 / Quadra 605.

Samsung 128MB 32x36-60ns ECC SIMM KMM53632000AK-6U

$13.50 each with free shipping

http://cgi.ebay.com/Samsung-128MB-32x36-60ns-ECC-SIMM-KMM53632000AK-6U_W0QQitemZ110331791958QQ

My guess is these would also work fine with the LC 575

The auction indicates the seller has more than 10 available.