You shouldn't ever need parts, but I imagine they are hard to get. I know there are several people on here with that exact model. If you're building a bench I find it easier to take off the big plate on the bottom and mount them right up to the edge of the bench. Like so... (the steel yard stick screwed to the bench is very handy too!)
I have 2 types, one like that one and a hand crimper. I like the hand crimpers mounted to the bench better, but my bench model has made a lot of snares over the years I did put a steel bushing in it after replacing the through-bolt a few times.