Springfield Leather is now selling Horween so that is a good resource in finding some.
http://springfieldleather.com/502/Horween/
Maverick leather in California has Horween. I have not purchased from them, but it looks good, has sales and seconds.
http://www.maverickleathercompany.com/#!horween
A couple pics and some more info.
I kinda went nuts as I could feel how special this leather was and know it is hard to come by.
Pic 1
These are the backs of three rolls
top=Blue Cavalier mid=Tan Cavalier and bottom= Chocolate Horse. All are Chromexels. You can see the waxiness in the back of the chocolate horse compared to the other two.
The Cavalier will make great bags and has a looser more flexible feel. All have the pull up effect that is easily rubbed out with friction. My son found that gorgeous blue stuff under a bench-so glad I brought him along that day! Blue will be a portfolio and a bag for my daughter. Tan will make a sweet bag. I have another chocolate roll I can't find the receipt for. I think it is also Cavalier and part of it is on it way to being a school portfolio for my son.
Pic 2
Two rolls (blue and tan) and two strips (black and chocolate)
The blue and the tan rolls on bottom show both front and back, they are the Cavaliers.
The black strip on bottom is an Essix, a form of Chromexel- it does not have the pull up effect and to me is in between density of the Horse strip and Cavalier.
The upper right is the Horse strip Chromexel in that beautiful chocolate brown. It is my favorite for color, feel, smell and workability. With its tight structure it cuts just sweet and is easy to edge. I made an angle card wallet out of a cut off and love it. No wax transfers to my clothes so far.
Happy leather working!!