Are there any volunteer HAA operators like volunteer ambulance associations?  Not local, count, state or federal government operated.  Purely volunteer. 

thank you in advance. 

County. Stupid auto correct. 

Almost all of the operators in the US are not government-operated if that's what you mean.

"Volunteer HAA"

2 problems with that- aircraft with stretchers, oxygen and staff, usually an experienced paramedic and a nurse.

Couple of things on this. There are plenty of non-profit organizations if that's what you mean... If you mean completely volunteer like some places in Europe, I don't know of any. Doesn't mean they don't exist but I don't know of any. I can think of one place that USED TO BE volunteer and completely funded by one individual and the pilots and rescue crews were volunteer and didn't charge for their work, but they are now affiliated with the county Sheriff and pilots and crews are Sheriff employees and I think their aircraft are now public use, and that's Two Bear in Montana. 

On ground ambulances and who are volunteer. Of course there are all volunteer fire departments that are staffed by all volunteer paramedics.