I recently just went through a month long debacle trying to get an obscure Grex part for my Tritium airbrush.
They don't sell direct, you have to order through the distributor. What I wasn't told is that they require their distributors to place a minimum order, I believe it's $250.
So I waited for my o ring to come in, which was so small I could not find it at a dozen different places around town. In fact I am still waiting to here from my hobby shop and every time I call, they don't know when it will come.
In the mean time, I contacted Grex directly and they sent the part out immediately, no charge. Not only that, but when I first emailed them to ask for help, I didn't know what was wrong with my airbrush, it was leaking paint from the trigger area. They responded right away with a detailed description of how it works and what to look for, and he basically diagnosed it through the email.
While I find the fact that they require a minimum order is frustrating, they responded right away and were extremely helpful. They even recommended a lubricant from a competing company to lube the new o ring. I would highly recommend Grex.
I have some extra .3mm fluid nozzles. I'm stupid and have damaged about 4 needles now, and they are freaking expensive. The nozzle comes with the needle kit. If you need a .3mm nozzle, I will be happy to send you one for no charge.
I am a beginner/novice with airbrushes, but I have been using the Grex for a while. I bought their hose and compressor, then added the thumb screw adjustment. This way I can set the regulator all the way up, then adjust the pressure at the handle my turning the knob. I used to obsess over what the PSI was and I could never get it right. Now I go off sound and feel, and try and always do a test. It has made a world of difference for me. You can get the thumb screw adjuster without their compressor, but I think you need their fittings and adapters. The PSI dropping is normal. You have to think, when you;re not pulling the trigger the system is closed, so the air builds up, to a certain point. When you pull the trigger, it is releasing the air, hence the pressure drop. Where the air PSI is with the trigger depressed is the pressure you are spraying at.