There are a lot of issues involved, primarily that I only make lamps as a hobby, and am 72 and like a laid back lifestyle.
I struggle to keep up with demand for the lamps as it is.
Looking at diving lamps. I have talked to divers and been acquainted with pressures as depth. Ouch
For a start a lamp would have to have a permanent fixed battery pack, hopefully one that an owner can replace cells easily. Ones produced appear to fit this criteria. The issue with detachable battery packs is that water would be forced up inside the cable. I wonder how many people realize this.
Moving on, second issue is the switch. Easy option here is of course magnetic, and if soft switching is used the current rating would be very low.
The seal on the battery pack would not be too much of a problem, but the pack would have to be CNC machined out of solid material. Cost.
Lamp itself, what remains is the cable gland and front lens.
Most lamps use polycarbonate which is machinable, but unfortunately will scuff and scratch over time which will affect the beam pattern, hence my preference for glass.
The bottom line on it all is that I could probably produce such a lamp but it would not end up much cheaper than dive Scurions.
A couple of weeks ago I had chance to see both a El Speleo and Phaethon, the former being described as waterproof to 40 metres, the later as suitable for up to a depth of 250 metres and tested to 7 bar. Both looked good to me.
I think that you have what you want there, unfortunately no UK agents which would be desirable.