Funny you should ask..... I think I got the last Factory tach from a dealer about 1 month ago. You can try e-bay, or have your local dealer do a nationwide search for you. It is a factory tach - Dodge part# - 82400711. The one on e-bay sold for around 250-300 i think. I found mine for 140. Try calling several dealers, you may get lucky. In looking at your signature, you have a 91. My 93 came pre-wired for a tach. All I had to do was plug it in! I don't think your 91 came with that luxury. Good Luck!
Mike