I used to buy it from local breweries. Almost all were universally helpful. Also very happy to give you some live yeast as well.
The last time I went though, they were reluctant to sell it (they said they get audited, and if the amount of beer going out is less than the grain coming in they get accused of bootlegging
). Given they were doing me a favour, I didn't want to push it. That was a couple of years ago though, so I may try it again next time I need to buy base malt.
I also work from home, so don't go past breweries on the way to work anymore