I think perhaps you have hit on the major downfall of this idea, a somewhat 'limited market'. Great idea on the face of it, I'm sure if I had a Sticky bomb without a cover and little chance of getting an original then at the right price I would consider a repro for display. But when you talk about making 100 sets then you need to find 100 owners of Sticky bombs missing covers to buy them. Even if as many as 10% of owners of Sticky bombs missing covers were to agree to purchase from you, then that would mean you would have to find 1,000 collectors who own them in the first place.
Not sure if I am making sense in this??, but perhaps you may find only ten or so people who would commit to buying one on the forum, however does this mean there isnt a market for them? They are not being manufactured as far as I am aware so thats a good start. I think perhaps if you were able to make a reproduction of the grenade itself (as you mentioned above) -together with the outer case itself, then it may appeal more to the re-enactor for display purposes as well, and in this way attract more people, rather than just owners of 'missing cover' Sticky's.
But as Dave says it all comes down to costs........maybe you need to work out how much it would cost to do first, before you try to find out how many people would be interested, because at the end of the day I think much of it would come down to what you can produce them for, retail.
hope this makes sense?
regards Kev