I'm sorry to say I've only ever made it to one Oz convention, and that was an Ozmopolitan convention about ten years ago in Wisconsin. I didn't get to attend the whole weekend, but was there for the day on Saturday and enjoyed myself - having read about the conventions for years, I was happy to see one in person.
One of the Saturday highlights, of course, is the Oz auction. I didn't have much luck at the auction, but did come away with one unique item - in a fit of desperation (perhaps?), I bought Dick Martin's typewriter. ?Why? I would never be able to say, but it was there and no one was bidding - and I must have been carried away by the moment. Anyway, a few dollars later it was mine and has been residing in my basement ever since! There are no signs of his ownership, and I couldn't say if he ever even used it - although it's clear that someone did.
Among his many Oz-related projects, Dick Martin did write and illustrate one Oz book. The Ozmapolitan of Oz was published by the International Wizard of Oz Club and is currently available in a new edition.