Kim,
I cant help you find that collet but, I was looking for R8 collets for 3/8-24 & 5/16-24 tap drills at work and ended up with a 10mm and everything with a 3/8 shank. I think mills have moved on to ER style collets. At the Zanesville show I bought a R8 to Morris taper2 so I could use the Jacobs 1/2 inch drill chuck from the lathe in the mill.
Art