I periodically receive queries about replacement decals for Lionel, American Flyer, or other "tinplate" models. I don't have them, but these people may:
East Coast Train Parts
P. O. Box 604
Englishtown, NJ 07726
(732) 972-8263
Charles F. Schmitt
1918 Minnow Creek Road
Annapolis, MD 21401
(410) 974-4736
eBay Sellers:
amberwing9 - See their decals
bggameboy - See their decals
trainplum - See their decals
yoderrr - See their decals
Something a little different: I met William Becker at the Timonium show and asked him about decals.
He says he does pad printing instead with custom rubber stamps and printers ink. (No decal film!) Check with him:
https://williamhbeckerinc.wixsite.com/trains
Wm. H. Becker, Inc.
P O Box I,
Havertown, PA 19083
WilliamHBeckerInc@gmail.com