Putting together an old Motobecane Nomade Sprint for my girlfriend and the seatpost measures out to be 24mm. Is there a 24mm aftermarket seatpost available? How annoying.

Is the clamp on 2-piece seatposts (non-integrated saddle clamp and seat post) a universal size? I'd like to at least replace the old 4-rail clamp for a 2-rail clamp.

I have an old moto mirage and the seatpost was 23.6mm but then had shim that fit in a 25.4mm hole. The problem was the seattube wasn't 25.4" all the way down, just the first couple inches. My solution was to buy a 22mm bmx seatpost and a 22 to 25.4 shim. If the only issue is the clamp I don't see why a 2 rail clamp wouldn't fit.

Exactly! This bike has the same shim and weird stepped seat tube i.d. except my crappy caliper measured the post to be right at 24mm. Did you try a 25.4 seatpost? Did it only go in a couple inches?

Ideally, I'd like to replace the entire post, but if an aftermarket 24mm err 23.6mm seatpost doesnt exist, I'll just be replacing the clamp so I can use a 2-rail saddle.

I couldn't find a 23.6mm but as my post was bent like a banana I needed to do the 22mm and shim thing. I tried to hone the seat tube out to 25.4 but gave up.