Good luck, I hope you find a solution. Honestly, it might be better to just stitch her new ones, or commission someone to do it (or, what I would do, would be to go for an outfit she wore in the show that they didn't make, LOL...I used to make or commission those outfits for my dolls because there weren't enough Misfit fashions.)
Jem stuff isn't that common in the UK now either, though I did see a few dolls at the toy fair a week or two back. I guess the show will always be more popular...
I have a cool Synergy repro outfit as well (one that looks like the show, rather than the weird doll leotard release) and I painted up a doll to go with it. I have a feeling that might've been Barb's fashions or something like that but she was in the US...not sure about in NZ but Etsy might be a place to check out? I know there are Etsy sellers who make repro Jem clothing for the IT dolls as I bought a Roxy doll with a replica of one of the outfits, but I don't know about the original sizings.