Good luck! Experimenting with different loads and bullets is one of the most fun things about having a muzzy. Here are some websites that I have ordered bullets/sabots/accessories from in the past. I don't have any particular preference- I just check all of them to see what is in stock and which site has it cheaper...

http://www.grafs.com/

http://www.midsouthshooterssupply.com/

http://www.natchezss.com/

http://www.midwayusa.com/