2008 Specialized Transition Pro Seatpost for Tall Long-Legged Cyclist

I'm currently scrambling to find a seatpost compatible with a 2008 Specialized Transition Pro that I bought from a private seller last weekend, as sort of an impulse buy. My local fitter said that the existing seatpost was just not going to cut it, and was a dealbreaker unless I can find one at least 400mm, preferably 450mm. I'm definitely a newbie, and have been scouring ebay, pinkbike, etc. to see if I can find anything that is compatible, but it's looking like the pickings are fairly slim.

Does anyone have any recommendations on compatible seatposts for this particular year/model that would work for taller cyclists (requiring a seatpost length in the 400mm - 450mm range) ? My research has given me a glimmer of hope that perhaps an S-works seatpost might work. However, at this point I'd just be happy to find something that is compatible (teardrop-shaped aero seatpost for 2008 Specialized Transition Pro, preferably w/offset, and definitely in the 400mm - 450mm range ).

Thx !