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.