4 1/2 x 4 1/2 x 10' wood posts? Oak or PT?

[bayviewsignworks]

We're trying to replicate a former signer's job where they used a 4.5"x4.5" x 10' wooden sign post. Does anyone know where I might source either PT, oak that size? They took the edges off each corner and their paint job doesn't have any cracks!

 

[Billct2]

I wouldn't use oak for that or PT if it's being painted.
A 6x6 cedar could be trimmed down.
A 4x4 PT can be wrapped with cedar boards to create a heavier post.
If you use 6x6 cedar you can cut the cost of the wood by using whgat I call a Cape Cod install (because that's where I learned it)
Pour a footing with a couple steel plates or angles that extend above ground a few feet and thru bolt the posts to these.

 

[fresh]

we always use pressure treated lumber, and I would guess that they probably were originally 6x6's that were planed down to that size.