If you know anyone who can sew, see if they'll do you a favor and put one together using your tartan fabric. I've been trying to convince my wife to do this for me, but can't find any decent material at the fabric store that I'd want a waistcoat made out of.

Look for Simplicity pattern no. 4762. It should cost around $9 for the pattern. If you don't know anyone who can sew, go to the fabric store and ask around. Surely someone there will be willing to do it for you at a nominal fee.