My experiences:
During the past year I have been on the "notify me when available" lists for powders at both Brownell's and MidwayUSA; I have not been notified about any powder availability from either company, which suggests to me I am still real far down on their waiting lists...
We have Cabelas, Scheel's, and Sportsmans Warehouse in my area.
I have never found any handgun powders at Cabelas.
At Scheels I have found CFE pistol, Silhouette, and HS6. They get in one pounders of HS6 real often.
Sportsmans Warehouse distributes an array of Alliant powders every couple of weeks or so. The local store has management that likes to play games, instructing its employees to stonewall regular customers who come in on known delivery days. Policy is to put powder out at random times so those of us who are serious can waste our time and gas while those who are not serious can just fall into it by pure chance. Still, I have managed to get Bullseye and Unique there...
It's a jungle.