I never have. Thus far I've been strictly an open-circuit diver. For some reason, I've have never had the disire to try one.
As for finding someone with whom to learn/do technical diving, I suggest contacting tech diving instructors in your area. Their contact information can be found by going to the web sites of the various training organizations. My one suggestion is NOT to get trained in Deep Air (a course that some agencies like PADI actually offer). I feel such training is dangerous and violates a key point in tech diving which is not to get Nitrogen Narcosis.