Go to
www.alliantpowder.com. I've seen Green Dot here and there, mostly 1# containers. But if you stick with it, you can make up some very good 3/4 oz loads and reduce pressures. The other components that you'd need are the Claybuster 1075-20 3/4 oz wads and Cheddite primers, both of which are readily available. Rem Gun Club or STS hulls. You'll be saving a grain of powder per load vs what you're dropping now. Especially if you're switching powder in the 20ga, where you have less margin for error than in the 12, you need to be cautious. The powder companies' guides are your friend. That 12.4 gr Green Dot load in a Rem hull with cheddite primer and 3/4 oz Claybuster wad is one that I've used a lot.