What brands do you refer to that are starting to sell directly? Aqualung, scubapro, oceanic and probably Sherwood will only sell parts to dealers directly, for sure. If you are finding parts elsewhere, they are not 'legitimate' and from Europe or shops going out of business. Good luck with parts coming from overseas- never know what youll get. A customer brought in a BRAND NEW regulator they got from the Internet (overseas) with a cut main piston ring. RIGHT OUT OF THE BOX. I fixed it and he paid for labor and kit.
Good luck with that- you'll end up with no-name bottom of the line regs. most new regs have free parts for life anyway. *(Sherwood has some of the most reasonable prices for repair kits of any reg I know of)
Shady backroom deals is not legitimate to me. BTW- are you selling parts on Ebay?
Depends what regulator you have but your right. Reg companies LOVE to create specialty tools that are necessary to test and tune some models. The AL Air Source comes to mind. Id guess that you will have the same hurdles getting these tools as you will with part kits.