How about buying a set of LEDs at different wavelengths and soldering them side-to-side? I know, it's not perfect, but it would be easy. The set could be: IR, 660 nm red, 625 nm bright red, orange, yellow, traditional dim yellowish-green "green", high-brightness 520-530 nm green, blue-green, blue (470 nm), deep blue (450 nm), UV (405 nm). Add trimmer pots to every LED and calibrate using a commercial panchromatic film with a known, published sensitivity curve.