You can find the C128 games at Arnold
http://arnold.c64.org (Arnold may be a bit hard to access, try anyway) and some games (freeware/public domain) can be found at Funet:
http://www.funet.fi/pub/cbm/
Oh, no one mentioned these: there are a few good games that run in the C128's 80 column mode including a very nice Solitare game and a pretty good Space Invaders clone. I believe they may be found on Funet.
Forgot to mention - the Elite 128 can be found at Funet too. It runs in the C64 mode but uses some coding tricks to get the game to run at 2MHZ.
Garak
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