Hey guys thanks for the replies. I understand I can take them anywhere that does scuba or fire station tanks. But from what I understand Flatline regs and possibly Nitroduck regs, because they are adjustable tanks, its not very easy to get the regs off. So they need to be sent to a hydrotester that knows how to take them apart and apparently the site I linked does, but they're in Washington State.
So am I wrong in thinking I need to find someone who knows Flatline and Nitroduck regs specifically?