If there is such a device it probably cost a ridiculous amount. For example, one of the larger photography stores in the U.S is selling "film canaster openers" for 20 bucks. Heck,I just use my trusty Moosehead Beer bottle opener.
I use a nice pair of curved manicure scissors. You could make a template of the leader from a factory film and use that to draw the correct shape onto your bulk roll and then cut.

Mike