you will get a 29.4 x 400mm seatpost from e-bay sellers for under a tenner
not a ringle/syncros etc but the right size
keep the shimmed one for the photos
probably because the already fragile frame will not like a shimmed post
i'm no expert but i have owned 4 rc200's that were in one piece when
i sold them
get a 400 + mm post if you can