You moght find one at Browning own web site,if not I would try gun broker.com,or e-bay.
Go to the link below for a download
You can request a owner's manual on the Browning web site. It also has sn data.
http://www.browning.com/products/manuals/index.asp
Please follow the cleaning instruction from the manual. The link is below
Your serial number indicates that your Browning light twelve was made in the year 1955.
Good shotgun
your browning auto-5 light twelve gauge was made in 1960.
Readily available from Browning.
your browning light weight 12ga was produced in 1960.
You will have to contact Browning to find out.
This is a Browning Auto-5 Lightweight 12 gauge shotgun.
The value of such light is approximately $10,000