Could you be more specific? 3T has several different seatpost designs, I think. I have one off a Felt TK1 that might be what you want. The "spline" part is worn, but the bit that holds the rails should be fine.

Sorry for not being more specific. It's a 20degree offset seat post. Made by Dorico. The bottom of the piece is half rounded, with the top being flat other than the groove that the seat rails sits in.

"Dorico" is Italian for Doric, as in the style of column (l'ordine dorico). The whole thing is made by 3T.

You'll more than likely pay more for the part (assuming 3T still stock it, which is a long shot b/c they discontinued it) than you would paying for any used post. Then again, doesn't hurt to try. Email them at: store@3tcycling.com. Note that if they do have it, it'll most likely be shipped from Italy (read, expensive shipping).

It sounds like the part to which you refer can be removed from the rest of the post. In which case, just get any 3T Dorico post and swap the part. Like the one below

https://www.ebay.com/...2:g:X04AAOSwxc5cnlCa

Here is the piece I'm looking for.

Yeah that is the plan if know on this forum has one lying around.

Thank you