I know of a place here in Glendale AZ that sells it. Matching the old stuff would be pretty hard to do though (I would think). Pretty hard to duplicate 25 years of weathering conditions on resin soaked/coated balsa.
If you can't find it closer to you, this guy has it. I saw it on the shelf the last time I went to buy my gelcoat.
Sticky Stuff
(623) 847-2444
6880 W Orangewood Ave
Glendale, AZ 85303
The owners name is Marvin.