Next to the Easyrider bikes, the "Then Came Bronson" Sportster is probably the next most commonly imitated bike. Still, you don't see that many. I found these photos on the web (Flicker?), taken outside the H-D museum.
The third one back is a replica of the H-D Sprint used sometimes in the show for stunts.
It really wouldn't be too hard to build one. Most I've seen are not completely correct.
These two are the closest to the real thing in the bunch. They both feature a correct 21" front wheel.