Using European Oxygen Bottle in DG-1000? Where to buy?

I've been reading the messages about the DG-400 oxygen system with some
interest.

In the DG-1000 that I often fly, we have a US oxygen bottle, the AL-647
listed on the Mountain High site:

http://www.mhoxygen.com/index.phtml?...product_id=359

The DG-1000 has a factory made oxygen cut out that can accept a bottle
up to 5.5 inches in diameter and 29 or 30 inches long. The AL-647 is
the only bottle that fits but is only 19" long. There appear to be no
other [longer] bottles with a similar diameter that we can get.

The problem is that even with a decent fill and the EDS system, two
pilots flying at high altitudes (16,000 feet or so) will run out in
about 6-7 hours with that tank.

Clearly it'd be good to have a bigger bottle. And since bottles,
relatively speaking, aren't that expensive, we're wondering if it makes
sense to order one from Europe and use it instead. It's be nice not to
run out and have to refill every single day.

Aside from the lack of a DOT sticker (the FBOs we use never look), are
there any other real downsides to this? Has anyone done it?

Where might I buy such a bottle or at least get pricing info?

Thanks,

Jeremy