A Kalloy seat post is very Low cost and is made in all diameters ... including 27.0mm
I used an adjustable reamer * and carefully shaved out the 0.1mm of wall thickness ,
in the 27.0 RB 1 I had owned since New.
* I used Cutting oil and only expanding the reamer a few thousandths at a Time ..
... until the post I had In Hand, Just Fit.
Of Course I cannot See the Bike You are speaking of..
FWIW UK USE had suspension seat posts in 25.0mm I had a AlAn with a 25.0 seat post ,
I used their sizing shim with a 25>27mm shim sleeve, initially ...
25.4 to all sorts of out side diameters in 0.2mm increments.. are made ..
I have 2 bikes with Oversize seat tubes and seat post shim sleeves .
so Yes get a 1" suspension seat post and then a sizing sleeve to get it to Fit.
Last edited by fietsbob; 01-23-16 at 04:30 PM.