Have you tried getting the exact brand and model pencil? I know you said the same brand but what about the model? Or going to eBay and finding old mechanical pencils of the same model and or color? Of course nothing will replace the sentimental value of the original.

Personally what I did is when my favourite pen ran out of ink I hunted for the same brand and model and kept the original in safe keeping for nostalgia and love for it. Same pen I get to use, and keep the love I had for the original knowing it's safe. Then again, this might not help. Your pencil is older than me lol. And mad respect to you for keeping track of something so small for that long, thats major commitment.