As Poly says, the vast majority of hydrostatic units in lifejackets out there are made by Hammar. However they only make the hydrostatic unit, not the jacket, which is I think is what the chap is asking. A quick email to them might give you an answer. Crewsaver have certainly been doing them for a fair old while.
Like Wilk I wouldn't bother buying one again (bought an expensive Crewsaver model back in 2006) - expensive to buy, and expensive and fiddly to service. I've never had any issues with the old salt/paper tab type.