Need source for window balance spring - old coil type - 50 years old

Hello,

My home was built in 1950, in southeast PA. It has wood sash, double hung windows with single pane glass. The sashes are supported (balanced) by long (approximately 30 inches long x 3/8" outside diameter) coil springs, fastened at the top to a screw in the jamb, and fastened at the bottom to a screw or feature in the sash.

The springs are simple extension coil-type springs.

I have searched this site and Google, and have only seen the spiral-type or what seem to be cartridge style balance springs for vinyl or tilt out windows. The sashes in my windows are not removeable, unless you remove the parting stop. It is unnecessary to remove the parting stop to access the springs in my window. It is in fact a very easy repair job, but I can't find a source for the springs.

Can anyone help with a source to purchase these springs? Thanks.

Found a picture, similar to what I have:

http://1.bp.blogspot.com/_wB-wKH0b9G...Window+Fix.jpg