I know of at least two 5100s out there that have one of the I/O expansion options. Unfortunately it is not mine.
5100s are hard to get your hands on. There was one on eBay that sold yesterday for just shy of $10,000; while it had the switches and keyboard keys for BASIC and APL both, it wasn't clear that APL was functional.
So far as I know, there have been no publicly archived 5100 tapes from IBM. The Computer History Museum in California has an APL tape in their archive, but they have not tried to image it. I have a few BASIC tapes with
sticky-shed syndrome and am waiting to do anything with them until I have a good plan for attempting data recovery. If you have any IBM software in your collection, you could have a rare item indeed, and it would be great to if it were archived.
In fact IBM 5100 tapes from any source may be interesting, if only to provide a view of what people did with the machines.
All of this said: it's virtually certain that your tapes are degraded in some way or another. At a minimum, the drive band that spins the tape reels will have broken. It would also not be unlikely for some of your tapes to be suffering sticky-shed syndrome too. All of which is to say: if you do get a 5100 of your own, inspect the tapes before you stick them into your machine!