I've got some surplus PCBs printed by online PCB printerer types;
0x Mahjongg ZX81+38 (r1.10) PCBs All gone!
0x ZX Team ZX81 Issue 1 (zx81a) replica PCBs All gone!
0x ZX Team ZX81 Issue 1 (zx81c) upgraded PCBs All gone!
I've assembled at least one of each type, and the only one I have issues with is the ZX81C. I used all brand new parts, but it refuses to boot. I think it's an issue with the ROM I've burned, or the jumper settings, or possibly the oscillator thingy. There's not a lot of documentation, unfortunately, and what there is tends to be inaccurate. Link to their project is here: https://github.com/Bluescreen2001/ZX81-PCB.
Looking to sell for £5 per PCB, plus £3 postage within the UK (can combine). I can probably post to the EU, but not sure what postage will be like. It'd be cheaper to source your own PCB if you're anywhere else.
I've got these listed on a certain other site, so I'll try to keep quantities updated if any sell there.
All now sold via an auction site