The local BORGs sell ROak and Poplar S4S.

It look's nice but, it's way overpriced, big surprise huh?

S3S (both sides and one edge) may be easier to find and work just
as well, since it most cases you'll need to cut to the needed width,
anyways.

The local Rockler usually has S3S ROak for $3.00/bf, maple was $4.00,
Poplar was also around $3.00 (or a bit less).

I've also purchased wood online and for a bit extra they'll usually joint
one or
both edges.

HTH

Ron