Measure the length from the end to the shoulder under the head.
Member "dtchb" has some in the classifieds that are 1.125" for $1.50 each shipped.
Philip and his wife are great people - give him a shout
S&W may even provide the grip scews free of charge. I ordered grip screws for my CS40 thinking I would have to pay. He took my name and address information and said "Have a great day!.
He and his partner own all the NOS forged parts that S&W were throwing out when they switched to mim. He is a great guy, and I am betting that he has exactly what you need.