I have this bridge and only operate it on rare occasions because the failure rate on the electronics is so high. In fact it's packed away now so I can't look at the parts.
Re: your question 1, I'm editing my original response because I might have misread your query.
Are you just looking to replace the original wall wart, i.e. this part:
This is rated as a 12vdc, 3 amp supply. A quick search on Amazon etc. reveals quite a few possible substitutes although (a) you might need one with multiple barrel tips to find what actually fits the input on the bridge's control box and (b) better check the bridge manual to see if it discloses the exact power input specs in light of what I say below.
Alternatively, there was an option to power the bridge from track/transformer power. You need to check the manual for exactly how to wire this. From memory it was not straightforward although I have used it.
if you are needing to replace the black control box, it's basically pot luck trying to find one. This bridge's manufacture was actually a sub-contract by Lionel to Mike Wolf of MTH and neither have access to a direct replacement (see linked thread below). Replacing the black box comes up every so often here and I recall a thread ending with a proposal by a forum member to create a substitute but I don't know whether he or anyone else did: https://ogrforum.com/...r-lionel-lift-bridge
I vaguely recall another thread where someone took the box apart to repair old components but can't track that one down. Hopefully someone else can weigh in with additional info if there is a substitute available. I'd certainly be interested in knowing if there is.
Question 2: I had to replace a tower strobe light on mine too, which came with incandescent bulbs on the towers. After reading about the delicate electronics I decided to source a screw-in incandescent bulb as a direct replacement instead of wiring for LEDs. These bulbs are easy to find; I think that they are basically the same size and spec as those used for K-Line illuminated bumpers.