O2 filling

With FBOs now charging $50-$100 to fill a tank I've started calling
around to see where else I can get O2 in the Sacramento area. It
appears that all the welding gas companies no longer fill bottles at
all. They exchange bottles and then send them off to a central plant
to refill. One company said they would not do it because they don't
have the equipment to provide some sort of "breathable" certificate
and would generate too much liability. The other welding O2 company
said it would take 3-4 weeks if they had to send my bottle out to the
main plant to be filled vs. exchange it for a welding tank.
I also called around for medical O2. Again, no one seems to fill
medical bottles. They all come to your house and exchange cylinders.

So has anyone successfully been able to fill an aviation bottle
anywhere other than an FBO? What about getting one medical bottle, and
filling from that everytime?

Interestingly, my grandmother uses O2 and she has an O2 generating
machine at her house (she fills her own portable bottles with medical
O2). However, the fittings for her cylinders don't look anything like
what I have.

-Robert