PM Shinobii. He's either got one in stock or can get one or (if you're really nice and a contributing member of society) he might pull one out of a stock gun in a pinch).

The last one I needed, I picked up...but I'm sure he prefers shipping them out for most cases.

He's bringing in a bunch of complete upper mechboxes as well...so that's a nice option to have in a pinch.

If the nozzle/cylinder head airseal is good...then it could well be the nozzle-rubber fit.

With the rifle fully assembled, I'd do the following in this order (least work to most involved):
1. Pull the barrel, reseat the existing hopup rubber. Reassemble and test.
2. Swap the hopup rubber, reassemble and test
3. Check the piston o-ring/cylinder compression, test
4. Swap upper into another rifle that's working reliably

Best of luck,

Tys

I also dont have the front mounted spring on the hop up (but I found a replacement), i hear varying opinions that it matters and that it doesnt, any confirmations?

pushes hop-up unit into the mechbox, provides better air seal. It matters. Or else the only thing holding it in place would be the mag.
Cut a few coils off of a spring-loaded pen... spring

The spring is pretty important. You can tell if that is affecting performance by manually pushing the hop up against the upper, if it fires better then that could be part of it.

How long should the spring be? I took one out of a pen but it keeps bending away whenever I put the hop unit back in.

It doesn't matter how long it is, but more or less how straight and wide it is. It should fit snugly on the hop up and point straight and not bend down.

Have added spring to hop unit, Chronied at a game to 335 FPS steadily.
Later I chronied it again, with the hop up on (shoulda turned it back off) 277FPS, but I believe the chrono may have died as I fired repeatedly but didnt get a refresh (and yes BBs were firing). I even turned it on and off and didnt get a number at all after.