My Evo is on the way from CZ Custom.
I just called CZ-USA re: availability of 30 round mags, they expect them "soon", 30 round magazine part number is 11350.
I also inquired about the original stock option, for SBR. CZ-USA is in the middle of 922 compliance paperwork, and "they hope" to have them, assuming the paperwork is approved.
So there is some risk in starting the NFA SBR paperwork before this issue is clarified.