I'm not %100 sure but wouldnt this be a no go for GMK due to the custom legends. GMK Cyrillic was done through pad printing. I know there is a number of people who did not mind it because of the uv coating but I hated it. If I'm right about this SP and JTK would be your only hopes
Edit
I read the post about Cyrillic not being viable so do you have anything else in mind for this set ?
I think we could make at least cyrillic alphas (modifiers excluded). Russian alphabet has 33 letters. 12 of these letters are available in latin. So i need to make 21 new legends. I asume a tkl version (in a standard GB) could cost between 120 and 150$. I think i am able to reverse engineer Gorton Modified Font from SP and make missing cyrillic letters. I have to scan those of course.
Lets go through the russian alphabet:
A - is available
Б - can be made out of B
B - is available
Г - upsidedown L
Д - This one has to be handmade
Е - is available
Ё - almost available
Ж - double K one is mirrored
З - 3 (three)
И - N mirror
Й - N mirror with this birdy
К - is available
Л - easy one is /\ tight together else handmade using I
М - is available
Н - is available
О - is available
П - two I top bound
Р - is available
С - is available
Т - is available
У - can be build out of Y
Ф - 0|0 or O|O cut and bound together
Х - is available
Ц - reverse П with tail
Ч - can be made out H
Ш - III bound at the bottom
Щ - same as Ш but with tail
Ъ - can be made out of B
Ы - B and I
Ь - reworked B
Э - reworked widened O
Ю - I and O bound together
Я - mirror R
So besically its doable but requires nice/perfect scans. And ofcourse is gorton modified and then it will be manufactured by SP. And costs hell a lot of money. But once its done it can be used for future projects by community. That was my plan so far.
As alternative we can frontprint them.