Although the conversion is relatively easy to do. To do it well on the other hand is a work of art and there are many ways to mess up your Saiga-12 especially if you are shortening the gas system.
I would recommend you just check out one of these dealers as they are reputable and have been doing conversions for years:
Companies that will do conversions on Saiga-12s:
TROMIX Corp -Tony is the best Saiga smith but not taking orders again till 2011 due to backorders
Rifle Dynamics- have seen good work come from there.
Cadiz Gun Works Office Phone: (740) 942-3175 - offers basic conversions.
Dinzag Arms - not seen their work personally
ISPC EoTach - not seen their work personally
Good places to get your mags and such here:
MD Arms (20-round Drum mag) -Mike is behind but is taking orders
Mississippi Auto Arms - Nathan takes care of his customers and has good prices on mags
Hope this helps.