For some reason, it's near impossible to find black HDPE, wide-mouthed bottles/jars, anywhere. You could use the bottles that hydrogen peroxide come in, but the mouth is gonna make that a pain in the rear.
PET (soda bottles) are also incredibly resistant to solvents and also highly insoluble to gases. Just keep out of sunlight.
Aways back I bought 7 1-lb cans of powder, rather than an 8 lb jug, just so I would have some extra cans. I got plenty.
You might have some extra jugs on hand that you just need to liberate. If you have 2 or 3 cans of a dense powder of the same lot, you can combine them. Or if you have any rarely used and near empty cans of powder, take what's left and pour that into a thick plastic bag or aforementioned styles of bottles and then put that into an opaque container. The vinyl sticker on these powder bottles peels right off, no problem. Put a big label on it, and there's really no issue. Grab an image off the net, resize, and use a color printer. Or heck, even draw something out with colored crayons and markers if you are worried about a mixup.