Source for high pressure fittings?

Hey all: Where is your "go to" source for high pressure (e.g. 5000 psi) air fittings? I'm trying to source parts for a bottle conversion (e.g. hex nipple NPT 1/8" and such) and want to get the proper pressure rated parts. Is it a spec or ASTM rating I should look for? I ordered a 316 stainless hex nipple off of ebay that stated rated for high pressure (with no PSI rating). I plan to experiment with a regulated ninja tank attached to my Prod guage port, but I would want that to be at least 3000psi rated. Thanks in advance. 


 
ebay and amazon is highly hit or miss on quality 'especially' with npt threads. .. i think the chinese dont quite understand the concept, for male fosters i'd get them from a reputable airgun supplier even if theyre a bit more to avoid a helluva time getting them sealed ... for other odd fittings t's and such, the best ones ive got so far were from 'hoseandfittings.com' .. i have a pile of unused bs fittings from fleabay though amd amazon is just as bad .. trust me .. dont go that way unless your sure ..
 
So my education begins on fittings. After reading the NPT specifications, as long as it's 316 stainless steel from a "reputable" supplier it should be rated for 5k psi, but the real issue is quality, especially in the threads. Poor ones don't seal. Is that the takeaway? I have a MVF fitting from ebay on order so I'll check it out. They appear to be a reputable supplier in Houston that supplied Swagelock in the past. We shall see.