Try....

http://www.pressalitgroup.com/index.html?language=eng

These people are a Danish company and are one of the biggest toilet
seat manufacturers in Europe. They have a UK office (see Dealer list on
website).
I do know that their seats are used by many 'heavy duty' installations
(eg motorway service stations, hospitals, etc.).
I have one at home and it is the 'Rolls-Royce' of toilet seats.
Cheers,
Jase