Sorry I misread I thought you said "imac", all of them besides the G4 and older g3 being slot loaders.
we ordered a lot of replacement optical drives from mcetech.com but they started having some customer relations problems so we don't use them much anymore. they do
write their own ODD firmware which is kinda interesting. Unfortunately makes it a pain if you need the driver discs again etc, because other companies were buying the same generic drives (JVC etc) and were pointing their customers to MCE to get the drivers, and MCE was not amused.