I dont know if you have ever tried this, and it may belong in the tips and tricks section, But...
If you invest in a small tube of "permatex Valve grinding compound" and just dab a small amount on the tip of your screwdriver, It will really help the removal of screws. Wrecked or not.
And +1 on Ace Hardware. I worked at an ace when i was 19. They seriously have the best selection of screws nuts and bolts, chrome plated, metric, whatever...
I completely rebuilt my 1968 Porsche and my 1975 CB550 and ace only let me down one or two times whilst looking fro replacement fasteners.