All our ones are old GU ones as well. When I work at Royal Brompton we had home made ones. Electrical safety testing these devices is intesting to say the least.
I would be intested if you find a supplier as the ones here are very long in the tooth. I would suggest St Jude or Medtronic as a starting point in the USA or Biotronic in Europe as they will be CE marked.
Only trying to help and spread the word