A lot of stuff like that turns up on eBay, you can give them a shot.
You can also try Numrich Arms/Gun Parts Corp.
They have a website and deal in used parts.
Sarco has them in stock there part # Misc119
1966
anywhere from $600 - $900
Your serial number indicates that your Winchester model 88 was made in the year 1967.
1971
Your serial number indicates that your Winchester model 88 lever action rifle was made in the year 1959.
The Winchester Model 88, chambered in .308 Winchester, was first introduced in 1955. The serial number can help determine the specific year of manufacture, as Winchester typically used a sequential numbering system. If you have the serial number, you can reference it against Winchester's production records or online databases to find the exact year of your rifle.
1962
In order to give you a more accurate value on your winchester model 88,I would need to know the caliber of the rifle,and what condition your rifle is in?
Your question cannot be answered unless you provide a serial number to the Winchester model 88 lever action rifle in question.
The gun was made in 1956
http://www.wisnersinc.com/additional_info/winchesterl_88_100.htm