Green Dot is not a good powder for low pressure loads. 800X works better but some don't like how it meters. If you go to the Hodgdon site you can figure several good load combinations and then have to round up the various components.
When looking for dead powders or ammo I look at small gun shops or gunshows as my go to place. Gunshows are mostly over priced but beggars can not be choosy. I have found many single pounds of discontinued powders or odd ammo lots from time to time. It is just as easy to look for odd things while looking for common stuff. I found PB by looking at a Facebook photo for a gun shop. The distinctive brown label gave me enough reason to call the shop. The owner confirmed that he did indeed have some PB and the price was fairly reasonable. But the problem was he would not ship it to me and he was four hours away. After a few minutes talking to him I found out his father in law lived less than 30 minutes from me and he could bring it down to me the next time the family met. So I gave him a credit card number and bought all that he had. Two weeks later I had my powder in hand.
