Been a long time since I worked with a Hiller, but at one time these folks did component overhaul/ repair on Hiller stuff:
Ft. Wolters Helicopters, Mineral Wells, TX,
Scott's Helicopters, Le Sueur, MN., (they worked on a lot of Hiller stuff back in the day)
Soloy (they changed their name around, but they're still in Washington state and still do some O/R)
and there's Hiller Aircraft somewhere out there in California - I never worked with them, but way back when Soloy sold the STC business to them they were doing lots of O/R on the Hiller side.
As I said, it's been a long while since I did any work with a Hiller and most of the ol' boys in the smaller shops I dealt with have moved on to one greener pasture or another.
Good luck.