erileykc,
I am not sure about the diameter of the original seat post, but given that the bike is such a good unit I would suggest that if you can find a steel seat post that fits into the frame to use it. If you need to have the adjustable function then you will need to create another clamping system. If the seat does not need to be adjusted, I would epoxy a steel/aluminium seat post in place and ride on. If you choose to epoxy a post in place and need some small adjust-ability use an old school seat post clamp that allows you to make adjustments on the tube by small increments. HTH, MH