Shadowran, I'm not sure if you are asking me or another poster. I used walnut mulch because I found it cheaper than the almond mulch. The trees are ground up in the orchards where they are pulled out. Most of the mulch goes to cogeneration plants to produce electricity. Almonds orchard are rapidly replacing pastureland. Deep water wells are drilled to supply all of the orchards and many, including me, are worried that our domestic wells will go dry as a result. Our water table has dropped significantly so this rainy season is a huge blessing. The mud, not so much.
Most almond hullers have almond hulls and shells available for sale. Some have contracts with other businesses that purchase all of the hulls or shells but many of the hullers will still sell to someone who only needs smaller quantities. I have at least 5 hullers within 2 miles of my house.
I'm sure that walnut shells are available but I don't know of any walnut hullers near me. I think that almond shells might be a bit better for the sheep than walnut because walnut shells are a lot harder and might be more likely to inflict cuts between their toes.
