nos parts

what does everybody do when looking for parts? if it is a foot operated dimmer switch, you go to napa,az,oboys,aap or wherever. what if part is not made anymore? where do you go now? i see a lot of parts on web when browsing. some are really high dollar. a pair of tail light lenses for a 69-71 dodge truck 90 ea used 220/pair new nos. it makes my wallet hurt. useed is okay most of the time but what if used not readily avail? just curious where people go now.