shoota 

~300m with setback, vintage preferred. Campy would be cool but not necessary. I'm more concerned with function, so I'd prefer the clamp to use allen bolts and not hex like on old Campy posts.

FOUND for now

Unca_Sam

I'm sorry to say that I've had this very problem, and 'vintage' (1995 and earlier) 26.6mm seatposts seem to max out under 300mm in usable extension. I have a saved search for 26.6 suntour XC posts, which give around 250mm of useful post. Road posts will rarely be longer than 180mm total. I suspect longer posts didn't come about until after wide use of sloping top tubes in frames. I hope you can find what you're looking for, though!

shoota 

That's really great to know! Yeah, my post is just shy of 200mm too.

These are the ones I'm looking at. Good price and over 200mm: https://www.ebay.com/itm/NOS-Vintage...IAAOSwGllaYkgd

IsleRide

As already mentioned, not likely you'll find anything that long in a vintage post. I'm looking for one too but in a shorter road bike version.
Here's a Kalloy Uno on ebay. Picture shows a short post but the description is for 350mm. Check with the seller.

https://www.ebay.com/itm/Kalloy-Uno-...53.m1438.l2649

shoota 

Yeah I learned that. But I got a couple options now. Are you looking for shiny silver? Or something else?

IsleRide

Just finishing up a Trek TX300 (actually a '79 310 but there really is no such thing) which is supposed to take a 26.8 but with the single butted Ishiwata Hi-ten the ID is 26.9 so that's too tight. Have a nice Campy NR 26.2 in there but that's too small. It's shimmed for now but want to get a 26.6.

Confirmed my frame takes a 26.8. Have additional info on ISO and For Trade sticky.

droppedandlost 

Thanks for that link, I need one too!

Unca_Sam

If you asked this question in the mechanics forum, they'd likely advise you to use the 26.8, or ask a shop to ream the seat tube. From what I remember, the heat needed to braze the seat cluster frequently distorts the seat tube, and a reaming to restore it to the correct dimensions isn't an uncommon task.

This is all assuming it's not just a pinched clamp area from previous use of an undersized post.

IsleRide

Probably from pinched clamp area as the bike came from the PO clamped down on the Campy 26.2. (I added a piece of handlebar shim) The bike is over 40 years old. Who knows what it was originally equipped with. I'm guessing 26.6 as usually there is more than .1 mm difference. This was a custom bike with butted Hi-ten. Not on Trek's build sheet in 1979.

Could be reamed as well. Good idea though, and may ask in the mechanics forum.

shoota 

Yeah I'd agree. A flex hone could do wonders on that seat tube.

IsleRide

And nice 26.8 posts are easier to find!