Are there conference interpreters on the market with no training?

Some experienced interpreters who never received formal training and learned by doing are still working today. They came to our profession when few training schools existed, as you rightly point out.

With excellent training opportunities today, it is inexcusable to inflict your learning curve on a client unless you really can't find a school that can teach your language combination. How do you know you're any good at it without any training? You need feedback from professionals who can compare your performance to what is expected in the booth and suggest ways to improve.

...here's one of those "unmentionables" who did not get any professional training whatsoever before first inflicting himself on inocent delegates, 34 years ago and counting :-). I've been trying to make ammends ever since, reading, watching/listening, ie learning as much as I can :-). I'm proud to say (not because I did pass but because it is my profession and I do see such openness as a lettre de noblesse) that despite my total lack of formal training I was allowed to sit an open competition for staff interpreters, because in 1985 the organisation which took me on expressly accepted "experience equivalent to training". This being said, it's only natural that as a profession establishes itself and its pedagogical tenets get progressively codified entrants come in by way of formal training, with all the benefits accruing therefrom...of which I was sorely envious as I fumbled along my way :-).