It turns out not many can issue a permit. I approached one of the 4 CASA delegates listed in WA with approvals for CASR 21.200 but the clauses applicable to special flight permits for maintenance are not included so he can't do it. Luckily I have now found one who can and is willing to issue the permit at a fixed cost less than the CASA estimate.
I'm still looking into Primary Category.
Re hours since last annual, it's actually done less than 50 hours. Don't ask me about economic justification for owning an aircraft. I don't want to even think about that.
CASA haven't given extensions to MRs, only medicals, AFRs and some other compliance stuff that doesn't apply to our small, simple aircraft. Maintenance organisations are still operating and happy to take your money.