There's always some on Gunbroker. That's where I bought all but my original one I bought in '94. I also bought all my extra barrels, forearm, scope, mounts, etc.
Sometimes you might have to watch for a few weeks/month(s) to get a nice one at a good price, but they are out there. Expect a nice example with minimal handling marks to go for at least $1,800 USD.
If you have an account, set up a "Saved Search". It will email you with new listings. Here's one if you want to use it:
https://www.gunbroker.com/Semi-Auto-Shotguns/search?Keywords=h%26k benelli super black eagle&PageSize=96&Sort=13&View=1