I usually bought powder in at least 3-5lb lots, or an 8lber. Over time it accumulated, and newer powders came along, some of those got acquired also, some haven't been touched yet.. The only thing I've had any issue with getting so far, was RL22, and I was in no panic for it. Only reason I didn't have enough for what I wanted, was that I didn't know it was the probable powder I'd need for one gun down the road, and the gun I'd originally got it for got sold, after using up a pound on it.
In the meantime, I have 3-4 others I can try out. I've had 2 lbs of RL22 all along, just isn't enough to work up a load and have a decent supply of the same lot, if it happens to be the powder that works the way I want it to. Picked up 2 more the other day, good to go now.
The US defense dept knows it has a potential problem with a production limitation, on the base stock of nitro cellulose supply, they only have one plant producing it, the other one shut down a few yrs back, the other plants are in Europe and Australia, ATK is a major shareholder in those also. With the current economic situation of the US gov't, it isn't likely they'll build another one, but, they'd like to.
Look at the new civilian ammo companies showing up over the last few yrs, they have been taking up quite a bit of the slack that was available in the powder market, that reduces the aftermarket availability for reloaders also. Two new shotshell mfgrs in Canada, Nosler in the US, HSM, probably a few others, Hornady expanded their products, the new cartridges that have shown up in the last 15-20 yrs. It all adds up in taking up the supply. The demand tripled or more a couple of yrs ago in the civilian market.
Liable to be like this for a while yet.