Im in need of the primary sear(?) and spring for a 642-2. i believe its the inital part connected to the hammer that begins the cylinder rotation. Due to arthritis, i managed to lose these parts. I found out the hammer is MIM!!! If you can help me out please let me know... su amigo, mexicanjoe

Try contacting S&W Customer Service. Have your serial number ready when you call.........1-800-331-0852

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Ret. LE, FA Instr, S&W Armorer

Not sure exactly which part you are needing but I would begin by checking a diagram or parts list to identify the exact part name and/or number. The link below is a start.
Next I would call Smith & Wesson with the needed info (1-800-331-0852) and they might provide the part for you.

"https://www.gunpartscorp.com/Manufacturers/SmithWesson-33495.htm"

Better be prepared for Smith to want the gun sent in so they can do the repair.