Back side of glove box, under or in the back of front seats, under or behind rear seats, under carpeting. Also heard of them under the rear package tray, behind sail panel, and behind the headliner. Barry Washington of the T/A Registry said he found one in a seat back rolled up in a ball the size of a walnut. So look close.
Check on MOPARTS.com, they have a lost and found for buildsheets, engines/trans. Galen might have yours.
Good luck and don't give up. Ray