I'm looking to swap out my excellent but giant and heavy PKA mount Vivitar Series1 105mm f/2.5 for a Pentax SMC or S-M-C (rubber or metal focus ring) 100mm f/4.0 lens. Don't care about cosmetic condition, really. I had an M 100 macro but now prefer M42 due to the magic A/M switch.
I have a fair bit of Pentax 35mm and 67 and some Canon gear if you might be interested in a trade of some kind.