Check professional rail magazines and product web pages. If you know the manufacturer of your unit, the better. Secondly, you might check with maintainers or even the stores department of you local railroad and ask if they could direct you to a source. And, yes, junk dealers, even antique stores, sometimes end up with things like that but I am assuming you don't have the time to do long term searching like that...but railfan flea markets and train shows would be a place to seek.
RIDEWITHMEHENRY is the name for our almost monthly day of riding trains and transit in either the NYCity or Philadelphia areas including all commuter lines, Amtrak, subways, light rail and trolleys, bus and ferries when warranted. No fees, just let us know you want to join the ride and pay your fares. Ask to be on our email list or find us on FB as RIDEWITHMEHENRY (all caps) to get descriptions of each outing.
Within the last month or so there was a post here from a fellow in SoCal (if I recall correctly) who had an "inside source" in the UP Signals Dept. for scrap signals, as he posted a photo of an ex-SP one that he had purchased, and was trying to figure out where it might have come from by the MP number. If you can find that post you could send him a Private Message/ start a "Conversation", and see if he has them or might know where you could get them . . .
There are also several websites of various collectors and fans, so you could try them, too.
Good luck with it !
- Paul North.
Our community is FREE to join. To participate you must either login or register for an account.