Benelli no longer makes this in .308 as far as I know. I originally bought this in .30-06, and it took me a long time to find a .308 barrel, which is what I have mounted currently. I bought it from Numrich Gun Parts; it looks like they currently have a 22" .308 barrel in stock for ~$700.
https://www.gunpartscorp.com/Categories/Barrels-35348/RifleBarrels-35346/308CalRifleBarrels-38426.htm