Occasionally can be found on eBay. Replacing the barrel on that model requires specialized tools, gauges and considerable gunsmthing ability.
Your Glenfield model 30A was made in the year 1979.
With the serial number that you have provided,your Glenfield model 30A was made in the year 1977.
1975
1976
1980.
Marlin Glenfield. http://www.marlinfirearms.com/About/History.aspx Marlin Glenfield http://www.marlinfirearms.com/About/History.aspx
With the serial number that you have supplied,your Marlin(Glenfield) rifle was made in the year 1980.
1978
1978. sales@countrygunsmith.net
Right below the hammer.
1978
Yes, I have one. The difference as far as I can tell is it has a lower capacity cartridge tube. Also they are harder to find than the 30A.