Del Selin's used to carry the sample packs.
I have no idea if he still does.
IMHO, they are a waste of money. Not enough powder to work up a decent load and make sure it will stay consistent under different conditions.
Another issue is that powder burn rates can vary quite a bit from lot to lot.
The sample packs look like a good idea but that's about it. In reality, you are much better off to look through a reloading manual, take a few notes about the powders you like the performance specs about, for the particular cartridge or cartridges you desire to reload. Once you have decided on which powders you like, buy a pound of each. If you can't afford to buy more than one pound, talk to a friend a split a pound.
Just remember, depending on which cartridge you're loading for, you may get less than 75 rounds out of a pound of powder. Pistol rounds are a different story, their loads are much smaller and you can get several hundred rounds out of a pound of powder. Same goes for small case rifle cartridges.