I ordered a replacement hammer for my 10-8 directly from S&W.
When I ruined the double-action sear (it didn't fit!) I ordered *just* the DA sear from numrich.
The Model 10 is a bit handicapped for bullseye due to the fixed sights and the short (for bullseye) barrel. A 6" model 14, 15, or 19 would be ideal (14 being the peach), but if my 10 was all I had, I'd shoot the heck out of it and be happy!
I find it hard to thumb-cock the hammer fast enough during the rapid fire strings, so DA is useful. Takes more practice, tho.
-Daizee