E-gunparts/gunpartscorp, gun shows, dealers whose specialty is C&R firearms.
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The CMP stores and website, you might find a few on Amazon and Ebay, and Cheaperthandirt.com. Vintage gunshops probably have parts, too.
your M1 garand serial number indicates your garand was made in 1939. the garand came about in 1936, so your rifle is a prize and would have significant value.
Your M1 garand was made in 1943.
Your springfield M1 garand was made in 1945.
Your M1 garand was made in 1944.
your M1 garand was made in 1954
Go to CMP to find M1 Garands and M1 Carbines. Also, go to http://www.m1garand.com, they will tell you everything...
Anywhere from $300 for a parts gun, up to over $1000
Your M1 garand was made in 1942.
By the serial number.
Your M1 garand was made in 1945.