On Track and AOPA do seminars mainly for FW FIs. On some, they invite a suitable rotary person to provide the RW input, so that an FI(H) can attend.
I believe that Geoff Day does do FI(H) seminars (see his website), that is just for heles. Typically, I think each outfit does only a couple every year. Presumably depends upon demand.
Having now attended a few of these, I would be interested to do a pure hele one myself. There is a lot of less than useful stuff for heles in the (mainly FW) seminars.