DG-400 Oxygen Bottle Problems

The only test and recertification station to serve Utah refuses to test
and fill the german factory bottles for the DG-400 since they do not
have a USA DOT stamp on them. The official regulations (which he
showed me) state that foreign bottles without the DOT stamp can only be
tested for "EXPORT" use. ie, airliner, ship, etc....leaving the USA
for its use. Oxygen suppliers theoretically should not even be filling
the bottles without the DOT stamp on them. I got two bottles out of
date and the last one nearing out of date ( so far I have local
airports filling them if the date stamp is ok, they don't know about
the DOT stamp requirement regarding refills.) On the DG-400 as most of
you know the bottle which has a smaller diameter than USA bottles and
fits in a fiberglass sleeve that threads its way from the cockpit past
the fuel tank without much room to spare. 90% of my flight time is on
Oxygen in the Rockies so it is getting critical to solve this stalmate
with oxygen bottle testing. DG-400 owners, what are you doing to solve
this problem???