I think the one on the NW corner of the BW @ 288 is Wayne's. I have never used them, but they also have a dirt yard at IH 45 @ Dixie Farm.
The one on the west side of 288 SB collector before you get to the BW is Higgins. I got grass from them years ago but never any dirt.
There is a living earth technologies on the south belt EB east of cullen. I think they have better organic qaulity soil and mulches that I hear advertised on Garden Line.
http://livingearth.net/