I'm sorry Erik....
I do not have a part number...
but I have a few ideas....
down on the bottom this forum site is the "for sale" topics.... put in a request that you are looking for one there.
Next go to our yahoo site.... Excelsriorhendersonresourceboard site.... and post that you are looking for one.... everyone there is friendly.
Even though the corbins are getting rare,.... I'm sure there are owners that have some just sitting around, and would like you sell them.
Also there are quite a few owners who have used outside vendors.... I'd advise you post another down below here, and the yahoo site to ask about other seat vendors and their opinions.
Myself, I've seen Aligator Bobs work..... and it is definitely worth the money, but its big money.
AND..... keep checkin ebay..... that's where we have found 2 corbins. Check it daily, because if it has buy it now on the tag, it'll be gone within a few hours....
Bruce