Curt,
Hello & Welcome to the Forum!
I've been doing a little research into your question, yes there are ways to supply the low voltage a/c current needed to test your locomotives, but the cost- time & money, make them impracticable.
(Hopefully someone will chime in with a wonderful inexpensive fix for you.)
Options:
Borrow a friends transformer.
Contact your LHS, you may inquire if they have a used, low priced transformer you can purchase.
a well used Marx usually runs $5.00-$10.00, or ask if you can bring your locomotives by if they have a test track.
If there is a train club locally contact them, I'm certain a member will allow you to bring your locomotives to their layout to test them.  Also a member may have an extra transformer they will sell you.
Then there's CraigsList, you can put an ad in their wanted section for a used a/c transformer.

If  none of the above works for you and you live in the boonies, or can see the boonies from your front porch like I can, PM me or catch me on the CHAT this weekend. Fri, Sat & Sun, 8-11:30 PM.

Dave