without pictures, I am guessing...
they are probably removable from the inside of the cab... (take a speaker out to get to the breaker)
a replacement breaker is probably available somewhere, but if not, something similar could take it's place with a little cab modifications...

Mahoning Valley Electric Service usually does a good job finding odd parts if you have trouble locating a replacement (but good idea to do your own search first),
you would need the info off the breaker (part number, manuf, voltage & current ratings...)
their number is (330) 783-0837