Have you left a note. I would tell him you are a collector and would take good care of it. Then offer an upgrade, a new 18 and a bag of charcoal. if this is on a regular route, I would leave a note everytime. Just a follow up to the orginal note telling him you are still interested and when he is ready to call you.
I have successfully done that six or seven times. I am working on a 50+ year old PK right now, she finally called back after 8 months and a half dozen notes.
Just get that grill!