Let's cover the entire list here:
Reshiram - If you'd trade it back as you said, this can be done. I haven't even used it yet outside of the final battles (and it fainted without a kill both times, mine must be weak).
Tornadus - Have (and it's mine, not traded in), but I go out for meals and use Wifi to trade; since Landorus is a biyatch to catch, I might be gone when you can trade back.
Heatmor - Don't have yet.
Accelgor/Escavalier - Their pre-evolved forms MUST be traded with each other to evolve them. There is no other way. Have a Shelmet and a Karrablast on standby for this one, though if you're all right with one not being your trainer ID, I can breed one or the other and you can have that one.
Crygonal - Can breed. I know it's rare and summer is nigh in-game.
Cincinno - Have one, but I can also get you its pre-evolved form if you want. I'm guessing you want to save the stone. FYI, however, it's found in shaking grass on Route 5 in place of Audino sometimes.
Whimsicott - I don't think I have a Sun Stone. I can get you Cottonee, however. If you play White, you can trade for one in Nacrene, too; have a Petilil ready.
Leavanny - Have a Sewaddle or a Swadloon? Swadloon evolves to Leavanny with high friendship. If you don't have the lower evolutions, I can breed one or you can get it from Pinwheel Forest in either game. Friendship resets with trading.
Swoobat - Also a friendship evolution from Woobat.
Panpour - I can get you one. Shaking grass in Pinwheel Forest as well.
So some of these you can do, but based on this info, let me know what I can get for you. My Unova Dex is complete including all Black/White exclusive Pokémon, and I'm working on the National Dex now.