I've bought a couple of these from the US on eBay.
http://www.mustangsurvival.com/professional/mac100?country=25
They are not sealed immersion suits but are designed to reduce cold shock / water flushing and keep you alive for longer. They also come with inflatable mitts and a neoprene balaclava.
The movement in them is very good but of course you do get quite warm.