I didn't know the "boot grip" was hard to find these days.
I keep a little box of rubber grips, I'll have to see if there are anymore in it.
Here's another good grip, Pachmayr Compac (Pachmayr® Pachmayr your primary source for quality handgun grips and recoil pads
The older ones look a little different and I'm always on the hunt for them.
Bought these here in the classifieds.
These fill in well behind the trigger and are shorter than other Pachmayr grips.