I forgot this, I looked into it a while back and the numbers 500-1500 correspond to the material used, I can't for the life of me remember what is was, so I was going to get some a try to make my own acrylic based stuff at home, mixing it as needed. I do that with bronze dust and microballoons, but the texture is much more coarse.
Anyway, all the places to source it from (I believe it was magnesium or aluminum powder) at a small enough quantity were catering to explosive target making supplies, so I decided against getting of that mailing list.