First the LGS is trying to rip you off. I bought the Apex kit, so I could always have the stock parts if needed. Go to the S&W website, you can order the whole sear assembly for the M&P 9c for around $31. The sear for the Shield is the same as the other M&P's. Not sure about the whole sear assembly, but you can just remove the sear. The Shield assembly might be smaller. The S&W website states:
Replacement parts and accessories for your Smith & Wesson firearm are available from your local Smith & Wesson Stocking Dealer, or directly from the Smith & Wesson Parts Department.
When ordering parts directly from the factory, please provide the following information:
•Model Number
•Dash Number
•Serial Number
•Approximate date of purchase
•Part view Number (refer to diagram)
•Complete Return Address
•VISA/Discover/MasterCard Number and Expiration Date
•For Foreign Orders Only, Fax Number or E-mail Address
1-800-331-0852 (USA)
Mon-Fri 8:00AM-8:00PM Eastern Time
They don't have the Shield parts manual up as they still won't sell Shield parts. Their parts manual is at:
http://www.smith-wesson.com/wcsstore/SmWesson2/upload/other/PistolPartsList_Retail.pdf
Bob