I use Ralph D'Alessandro in Brooklyn. He does business on eBay as Radtrains. If you do an eBay search on "Lionel 180-181-182 decals", you will find him. He has a couple of hundred sets of decals for prewar Lionel, Ives and AF. I just bought the 180-181-182 set from him - $12.50.
BUT WAIT UNTIL June 1. He's on vacation and his site returns 0 entries today.
I've bought many set from him. A good supplier.