This is probably the most viable choice....as it's available by the foot on amazon.
I have searched for this stuff before and never found one available to the 'layman'.
Great info on the product too.
It's funny, I used to work in an extrusion plant that made this stuff, we called it 'pinch welt'.
The others seem to be industrial sources that usually only deal in large quantities to industrial customers.
Glass shops might have it.