not sure if this might be of help....u can contact them (at bottom of the page) and they might be able to stir u in right direction on locating it, from my understanding the lens is pricey....i just obtained a 2001 dts and it has it and when i was doing some research i stumbled on this....another source....would be a bone yard (proably slim, but worth a chance) alot of boneyards now have that computer search deal (if they dont have it they can locate it) good luck
http://www.marlow.com/Applications/DSP/cadillac_night_vision_system.htm
http://www.marlow.com/Applications/DSP/cadillac_night_vision_system.htm