If 2006 55s are out, tell them to try to get a 2005 55.
If that doesn't work, tell them (or their Lemond rep) to call around other Lemond dealers in the area and see if anyone else has a 55 in stock still that can get sent to the shop you ordered from.

I wouldn't begin to talk about fitting the 53 until you've exhausted all other options w/ trying to find the 55.