I think Daniel Smith has a synthetic brush that is a re-branded Richeson. And i believe you can google for Dixie Art supplies for the lowest mail order price on the Richeson. (wish I had known when I bought mine)
If you are doing 4x5 and 8x10 photos, i would recommend the 2" brush. I found out recently when I was doing some 4x5 test strips that it IS possible to have a brush that is too large for your print size. The problem comes in because the richeson brush is used soaking wet, and a brush whose water volume is much greater than the sensitizer volume will dilute your coating mix too much and result in weak prints. For 8x10 and smaller, the 2 " is about right. For 8x10 through 7x17, the 3" is about right, and for 12x20 and larger, the 4" brush is useful.