No, I'm not 100% sure about either Zeagle nor Atomics....it just seems I've seen reps from those companies state that they are made in the USA.
As far as the TUSA reg though, it is the same as a Scuba Pro Air 2, not the Zeagle.
Second
I find it hard to believe that Zeagle regulators are made in the USA. When I bought my Zeagle DS-V -- I don't recall seeing any 'made in USA' marking on the carton, there is no 'made in USA' marking on the product, however, it did come with a LP hose marked "Ocean Divers Supply".
Load up google maps, go to the zeagle address and look at the building in Satellite view. That roof doesn't look like the roof of a manufacturing facility. And, the building looks like it's just big enough to hold some offices and a little bit of inventory.
Having worked for both domestic manufacturers and import businesses, I know domestic makers are big on marking everything with 'Made in USA' - when they can do so legally. I also know that importers have ways of hiding country of origin.
As for the SP 3rd gen and TUSA alt air, I think it was DA Aqualung who said they were the same? Looks like it. I downloaded the service manual for the SP 3rd / 4th generation. I own the Alt Air made by Ocean Divers Supply (private labeled for several US companies). I disassembled my ODS Alt Air and compared it to the SP 3rd gen service manual - they're the same. Actual the only difference I noticed was that the one I have has a bezel that secures the purge cover - it's a little different than the SP 3rd gen design. But aside from that - they same thing.
Incidentally, my Alt Air - private labeled 'H2odyssey' and made by ODS, has no country of origin marking.
I presume that ODS is importing components to their facility in Southern California. You can import components without country of origin marking. They probably then assemble for any number of US brands (H2odyssey [ located in the same building as ODS USA], Dive Rite, Dolphin Scuba Center, Leisurepro (for their Blue Reef line), ScubaMax, etc). It's just a guess, but I've seen other businesses run this way.
I think highly of Zeagle. I've got several of their regs and one of their BCs. Their staff and the support they provide are as good or better than anything else you'll find in the Scuba industry. They support both 'users' and 'dealers'. However, if they're making regs in the States, I'd like to see pictures of the mfr facility. Until then, I'll remain skeptical.