Piston/Chamber/Nozzle upgrades for G&P gearbox?

[Kali]

I've got a project gun with one of the stock G&P gearboxes you can buy in it, and I'm looking to improve the air seal and compression. I know the stock parts aren't likely to be great, so I'm looking for some suggestions on some replacements.

I've already gotten a ProWin hop unit and a Madbull barrel that I'm hoping to use with it, so a nozzle compatible with the ProWin unit would be ideal. As for the rest of it, I'm just looking for any decent parts.

Cheers.