Isolated bidirectional Buck/Boost transformer
You might look at the documentation for the LT8584 cell balancing IC.  They talk about flyback transformer selection (built-in inductance) and give some examples that are approximately at the voltage range you're interested in.

In general though, unfortunately SMPS transformers don't tend to be stock items (with a few exceptions).  Often you have to get a manufacturer to do a custom run.  This isn't quite as painful and expensive as you might initially think.