[SEL] Oak wood for carts

[Curt]

Guys,
I am having a little trouble finding oak lumber to make the carts rails 
for the Baker Monitor project we are working on. I am looking for oak 
that is dried/cured that will finish to 3 1/2" wide x 5" tall x 48" 
long. Will need two rails. I have called all the lumber yards in the 
area with no luck.
A lot of you use heavy oak timbers on your carts and I am wondering 
where you find your wood. Dave Rotigel has some huge timbers under most 
of his engines. Your source?
I appreciate your suggestions.
Does any of you have wood this size for sale?
Curt Holland
Gastonia, NC