Find your nearest welding shop, make friends with "the guy" there, and have him do your fills. The O2 they have there is every bit as breathable as any other source (medical, aviation, etc.), due mainly to the fact that the same O2 cleaning standards apply. This has been my source of O2 for blending trimix for years, and I suspect is the same source for the LDS near me who stocks O2 for PP blending Nitrox and filling O2 cylinders for customers.