Shouldn't be an issue, all of my radio systems have included a battery holder for the receiver. If you are buying used parts here and there, just ask about it. I know I have several laying around that I've never used except for occasional troubleshooting. If someone is selling used stuff they probably have them too. Or shops sell them for like $5.

I may be wrong, but I thought the different plugs were history, doesn't everyone use Futaba J compatible plugs on servos and esc nowdays?

And I strongly agree with cbd that a local hobby shop is a good place to go. Just because it's online doesn't automatically make it cheaper. Sometimes this stuff doesn't work, a good shop will take care of it. Shops frequently have used stuff, or know a regular customer that does. Ask around, look for bulletin boards, hang around race tracks.