Haven't seen Regulators with RD-40 / DIN EN 148-1 screw mount in quite a while.
Most of that equipment I've seen uses M45x3 [DIN EN 148-3] and overpressure regulators... [1]
But there are constant-flow units for that too... [2] I'm just not shure if the manufacturer actually tested those for use underwater / at above surface pressure...
1: https://ekastushop.de/en/scba-diablo-rina-1800-marine-type-2
2: https://ekastushop.de/en/compressed-air-line-unit-airline-fc-1002-basic