Sounds like the same kind of thing that happens to workers
hands where the same tool is used daily.

I'm assuming that your crutches are those "standard" ones
with the wooden hand-grips? You could try looking around for
moulded grips that would spread the load more evenly, maybe
ripping some of some other tool and gluing it onto your
existing hand-grips, or even upgrading your crutches to
something a little more 21st century maybe? If that exists
of course. :\

Here in the UK, I've only found those temp crutches for
injury recovery that have moulded handles. You'd think that
the long-term ones would be better, but...

More info on your crutch type (!?!) would help...

Donna - I agree with Mike about maybe switching to another type of
crutch but if that's not an option, how about a glove with the fingers
cut out that are used by folks who use manual wheelchairs on a regular
basis?  That would protect your hands from the callus in the first
place as well as give you a better grip.

When I was on crutches a few years ago I used what were referred to as
"Canadian Crutches"  I called them forearm crutches because that's
where they supported on the forearms instead of the armpit. Still had a
grip problem though. I'm really bad with crutches.  Very weak in the
upper and now the lower body for that matter.

DianeW