you can try places like www.cluboverclocker.com. but most sites that sold overclocked hardware like oczstore, and such shut down due to you pay a premium price for buying stuff pre-overclocked or modified
just look at modded PS2's they can cost 600 bucks! so if you rally want the speed, just buy a faster proc, or read all the guides, pray and try yourself
yeah, yesterday i went ahead and bought an athlon unlocking kit. all i really need is that conductive lacquer but it's so hard to find.
lol... at the same time, i bought a 1.4ghz proc! totally defeats the purpose of overclocking since my board doesn't support faster than 1.4. but i have a couple friends that wanna unlock their athlons, so i'll practice on my 800.
also, bought a ti 4200! good ol' tax refund came in handy.