CeeGro: 1975-76. Numrich lists a variety of options for replacement slides in nickel (not silver) finish - I believe they're all used rather than new, but perhaps that's not a problem for you. Is the slide missing or damaged beyond repair? Even though replacements are not too expensive, you might have cheaper options.
Parts for your gun here: http://www.gunpartscorp.com/catalog/...spx?catid=9881