If you find one of the PIII heatsink/fan units that support 900MHz and 1GHz then you can use it on all of them as PIII's at those higher speeds are supposed to have a higher quality/performance cooling solution than the slower PIII's. Took me a while to find a heatsink/fan that was specifically rated for those higher speeds for my PIII 1GHz but a found a vendor that had them and picked one up and a few extras just in I needed them for a future project. They are really nice being copper based and have a detailed heatsink design rather than just a slab of aluminum with some fins on it.
Roland MT-32 (old), CM-32LN, SC-55, SC-88VL, MT-120, SD-35, SD-20, SD-80, SD-90
Yamaha TG100, TG300, MDF2, MU15, MU100, MU2000EX + PLG150-DR + PLG150-PF + PLG150-VL
KORG NS5R, X5DR
AKAI SG01k
KAWAI GMega
KETRON SD2