Possibly gestalt based therapy, though they may try to talk you into thinking that your people are not actually individuals, but other aspects of yourself. I also had one, who had a base in somatic or body therapy that never suggested integrating. I'm afraid though for the most part, you just have to keep searching until you find a good one, younger folk seemed to be more open, but then there is the trade of with their experience levels and if they are in there internship period, they may have to go elsewhere in a fairly short time period.

I have yet to talk to a multiple for whom integration was a successful or even helpful strategy myself. It would be nice if "formal training" caught up with that.