Thanks to all that responded. Hopefully I'll have sourced some this week form the recommendations you've passed along. I'm looking for a large quantity so I'll never need to go looking for more, at least as long as I own the rifle.
Jason Spencer will be building the rifle for me from a BSA Martini model 12 that has been bubba'd by the previous owner. I had an old Model 6 in 22 Hornet but reloading the brass is a delicate venture so I thought I would try a 218 Mashburn Bee with its more stout brass.
I'll post pics once it's done.
Cheers!