I've been looking for a miniature like that for a very long time, and it's frustrating to see it appear at the last minute tacked on to a terrain-based IGG campaign .
Obviously in your particular case it won't work at all, but this
is a terrain campaign and the miniatures are currently just a little extra, primarily for people who have already paid for 10 kg of resin and its shipping.
It already says they'll be available for 36e afterwards so not limited edition by any means. No idea whether you'll be able to get single minis (or multiple copies), but in reality the answer is usually "yes" if you simply write and ask. (I'd like to know, though, what's so special about that mini. Aren't there boatloads of archer-adventurers out there? Just wondering...)
Meanwhile, I just bought a set of those stone sheets out of curiosity. We play a lot of urban skirmish games here and if these are even half good, they look like a viable solution to many persistent problems.