check your local gunshops get what you can to start shooting, then check the net, google 7.62x54r ammo, check http://www.centerfiresystems.com, http://www.cheaperthendirt.com, http://www.natchzss.com there are more lot more I know, but can't think of the address' right now. when you order from any compenys add $20 for hazmat fees to be safe.

centerfire systems just charges shipping, $9.99 - 12 they are a zone shipper that is up to 300 rounds. they have BAG of 20 rds for $4.99 and 10+ is 4.50/BAG.
they also have sellier & bellot 180gr fmj 20 rds 14.99 and 180 gr sp 20rds 18.99. I never ordered from them so I can't tell ya how they are, I had there flier on my desk