You can try ytmag.com.. or sometime the pulloff.com site will have a few antiques for sale...
I'd build an A before the B's.. the B's can be fun.. but its easier to get the HP in the A's.. You can build an A big... there are a few working on some custom blocks for the B's that will allow them to get some big cubes.. but most in the developement stage.. But just a 5.75 bore 9-9.5 A is not too hard to build.. and will run strong...
Good Luck...
Bryan