velorinka,
Welcome to the Classic and Vintage forum. Glad you stopped in!
Unbelievable that in this day and age, that anyone would steal Schwinn steel wheels!
IIRC, one of our members at some point installed MTB wheels on a Varsity which required 27" wheels, so it can be done. But, again IIRC, he had to use hub brakes because calipers could not reach the smaller diameter rims. I'm guessing you will have the same issue.
Another issue you will probably encounter is that the Varsity front hub is not spaced at a standard 100mm. Instead it is something like 95mm. That might not seem like much but it does impact how the front hub fits in the fork.
So I hate to discourage you, but your best bet might be to begin a search on CL and see what you can find.