MTV Classic (formerly VH1 Classic) used to show a lot of Beach Boys content, such as the Knebworth concert and Brian's Pet Sounds Live from 2002 though I haven't seen much of that sort recently. I know the AXS channel recently ran a Beach Boys marathon though my provider doesn't carry that channel.
They also used to show the American Family movie a lot. I recall, as recently as 2012, they did a Beach Boys Weekend for July 4, which consisted of Knebworth 80, American Family, MTV era videos, and I think The Lost Concert.