I got a citabria 80" wingspan, but it doesn't have a windshield.
Is there a website where I could get this part, or, is there a way I could fabricate this?

Make a template out of some card stock. Basically try to make a shape out of the card stock that will fit along the top of the fuselage ahead of the cockpit area, then wrap around the side of the fuselage. You going to have to make a cut that will fit along the shape of the airfoil at the top of the cockpit/fuselage area. You'll have to use #2 screws or what ever you use to secure the windshield on the sides and across the top.