Yep I second that, we have a Nelson 42 at work which was built by Halmatic but I think the original contacts we had have long since lapsed.
As said above, VT and BAE Systems became BVT and are now Babcock - they operate down here and I deal with them a bit at work for various things.
The rights to build the Nelson hulls appear to have been bought by Seaward Marine Ltd but not sure about the other stuff like RTK - there are a few RTK Sea Trucks here but certainly nothing less than 10yrs old. BVT now build some of the RIBs - there was a tasty one in RIB International recently, a 9.5m with two Volvo D6 diesels