Is there a website that sells every single type of spare part for the M82? so people like me who can't afford to shell out 8 grand on the fly can buy it part by part and assemble it myself?

This sort of question has come up before in this forum. It was mentioned that Barrett rarely, if ever, sells the receiver separately. This would be your biggest obstacle.

Save your pennies or get a loan. Ronnie Barrett will only sell a factory built rifle, not parts kits or receivers (at least to the gun-owning public). Been there done that, so I scoured GunsAmerica until I found one I could afford.

After owning the M82A1 for over 3 years now, I can see why Barrett is skiddish about "parting out" their weapon. There is the possibility that someone could partially build an M82, and if one part is left out/off (such as the muzzle brake) there is a definite chance for disability if one should fire the thing without it being completely built. For some, human nature and a lack of patience can and probably would take over..."I can't wait to try this thing out, I don't need every recoil spring..."

The result would certainly be some lawsuit against Barrett, ("Barrett knowingly produced a product that was too dangerous for the general public to build", etc, etc, etc...). So, as much as I know you probably wouldn't shoot the thing until every part was in place, you & I know the types who wouldn't wait. I'd have probably been tempted myself, to be honest.

The 50BMG is nothing to trifle with. It is one friggin' powerful cartridge, and a lot of thought and engineering went into the 82A1 to make it safe to shoot as a stand-alone semi auto rifle as opposed to having to own an 80# Ma in a pintle. One can only get a real understanding of what you're dealing with when you chamber something designed to shoot a half-inch 650+ grain bullet at better than 2500 fps. Pulling the trigger the first time is a bit hairy. Cleaning the heavy chunks of steel that make up the bolt/barrel and other assemblies really give you an appreciation for what it takes to tame the beast of a detonation that happens within its chamber. Awesome doesn't even come close.

As I said, save the pennies and buy the whole enchilada. It's worth every hard cent.

I heard, probably an  urban legend,  they did sell receivers at one point to people in Kalifornia to get them registered before the 50 ban, but you had to send them back to have them assembled. Liability to have someone other than them assemble it would be too great.

I doubt they sent the receiver...that just wouldn't make any sense. More likely, the Kalifornians purchased a "serial number" from Barrett that would later be built/put on a rifle. I seriously doubt Barrett would send a receiver & trust that they would be getting it back.

Never heard that legend, but not impossible, I suppose.