Quoted from ForceFlow:

New ones? No.
Transformers do pop up on ebay occasionally.
You'll need an E-122-142 transformer.
http://pinwiki.com/wiki/index.php?title=Bally/Stern#Bally
But, you might get lucky if the problem is on the rectifier board, rather than with the actual transformer.

Quoted from dasvis:

I doubt that the transformer is bad. Very-very seldom is this the issue..
Read the pin-wiki, or find Clay's old guide on -35 pins. More likely a problem with the rectifier board.

Quoted from xTheBlackKnightx:

In reference to Bally AS-2518-54 Rectifier Board A2 Assembly (EBD board version 2):
I have only seen three? transformers have problems in nearly 30 years.
One was caused by crystallized solder joints, so not directly the transformer after all connections were reflowed.
Another was inside the windings due to an electrical strike through a cabinet MOV, so the transformer was toast.
The third was short circuited by owner hacking connectors, so the transformer was toast.
Common problems:
High Current Fuse Clips
Bridge Rectifiers w/ Wires (200V 35A)
IN4007 diodes
100 Volt MOV
Careful when voltage testing, the current can kill. Keep a family member nearby with a wooden stick
Once you verify the test points, rebuild the board, unless it is a hot mess.
If you are really in pickle, and the transformer truly is bad, remember video arcade games from the 80s used the same transformers in many cases.

Quoted from Pbpins:

Yes, they do exist, I have a few good transformers!

Quoted from greatwichjohn:

I have seen a few transformers go bad.