Bullets are easy, brass is hard. I got a lot of my brass from ammobrasstrader. com. I also bought a pile when Smokewagon gear had JMS headstamped fully loaded 7.62X54R ammo for 5 bucks/20. They were Boxer primed and I been reloading them since. Sadly, no longer available. I have JMS, Norma, Lapua, Winchester, Prvi Partizan, and S&B brass.
Any bullet for .303 Brits work fine. A lot of people just use .308" projectiles and say they have no problems, but none of my Mosins bores slug out that low, so I use .311-.312" bullets. Right now I bought 2000 pulled .311" 147 grain FMJBT's, and I expect I'll be shooting them for a long time. I use cheap milsurp for plinking, and my reloads if I want to see how accurate I can shoot the rifle.