Does anyone know where i can get parts for the 669 9mm.
specifically a new backstrap and lower dowel pin. If there is aluminum not plastic version that would be even better!

Thank you in advance.

Looked at Numrich Gun Parts which usually stocks older parts, but looks like out of stock on this item. Says to check back in 30-60 days which may not help you now if you need it soon. Schematics may help you find the particular part as name or part number(appears to be part 99)
Here is link to schematic and part. Numrich Gun Parts Corp. - The World's Largest Supplier of Firearms Parts and Accessories

There is one on Gunbroker.com for $25.

Have you tried the S&W Factory.
Call their customer service.