I know this is kind of a silly idea, with the XF100 being so small, but there are times when I really need ability to move around quickly but still get relatively stable footage (at least some that I can stabilize in AE or Motion).

Normally I'd be tripod mounted for ultimate stability, going with a steadycam is not an option (several reasons) so shoulder mount is about all that's left (hand held is too unsteady).

So, suggestions for models to look at?

You might check with Olaf Eckberg, Westside AV, a sponsor here and a frequent contributor. I don't know for sure if his mounts fit the 100 but it would seem logical and if not perhaps he could do a bit of mod to it.
While I haven't used the rig it appears to be a great build quality and fairly priced.
Just a thought.

How about a monopod?

On the cheap: Spiderbrace. Works well with my XF-100.....not the XF 300 though.