Call the Train store in Leonardtown where the ace was at in the small shopping center where Salsa's is on RT 5.. They sell new Lionel trains there and I would be surprised if they didn't work on them or know of someone that did.
It used to take up the back stockrooms and a second floor in the back when the hardware store was open there..
It's normally the owner that's there, he owns that and the ace in Charlotte hall and Leonardtown. Good guy..
.edit, I just talked to my son who worked at the Leonardtown Ace through HS for Marty.
The train store was moved to where the new store is now located at. To the left of the hardware store entrance there is a door that says some home decorating business, you open that door and go upstairs and thats where the train store is located now.
My son said he will stop by tomorrow if he remembers and ask the boss man if they or someone they know work on them.
If I could locate the exact coupler needed maybe. A quick Google search last night didn't reveal any though. Besides, this is a 1962/63 locomotive in very good condition (with the exception of a missing coupler of course). I have no problem with someone versed in Lionel repair doing the work.
I just spoke to the guy at SideTrack Hobbies in Leonardtown. They are no longer an official Lionel Service Center and will not service "contemporary" equipment, but still perform service work on "traditional" equipment. My loco qualifies as traditional.