Quoted from cynric:
Don't worry too much. From my experience with that shop their products are very often of less-than-optimal quality; regarding repro plastics I have no own experience but I've heard that they follow suit.. As you only need sling shot plastics they should not be too hard to get NOS, I've seen them quite often for sale in the German forums.
I'll take a look when I'm at my JM next, if I've got an extra set (not sure if I've bought one) I can offer that as a backup. A single letter to the States isn't that expensive..
Thanks for the help. Much appreciated!