I've always run Avid bearings on other cars... just bought a "set" for the Losi (you have to look them up individually and order them of course... sizes are in the manual, just read through the assembly and the sizes are marked.) And I ordered 10 sets (20 bearings, 10 of each size) for the clutch bell.
We blow the clutch bearings out with compressed air before running... otherwise you'll have grease on your clutch shoes.