I have had about a dozen people approach me through chat, email, and Unfiction private message. All of these contacts have started out with “I have a couple of really good ideas for puzzle cards, how did you submit your ideas to Mind Candy?”
In an effort to not repeat myself so much, here is a summary that I can point people toward. Back in the day when Perplex City was not even called Perplex City, but Project Syzygy (more info) and was more of an advertisement for an unnamed upcoming ARG rather than an ARG itself, they put out a call for puzzle designers. I was not one of them. Nope, I didn’t apply. That was in 2004.
In 2005, ARGfest rolled around. Because of prior commitments and financial reasons, I was not able to attend. Rose did an excellent job of not only arranging activities, but also arranging decorations in the stark conference room in which talks were hosted. Some of those decorations were posters paying homage to ARGs of the past and present. Because I could not attend, I thought I would try to be there in spirit by volunteering to craft a poster for Perplex City. The one I made looked suspiciously like a puzzle card.
After ARGfest, both Michael and Adrian contacted me through email to thank me for the poster. Further conversation happened and I eventually found myself as a freelancer, designing a couple of cards. The rest, I guess, is history. I am told that Rose packaged up the poster and shipped it to Mind Candy and it is hanging on the walls there. (Good thing they didn’t notice the hidden microphone spying on all of their top secret conversations! Muhahahahaha!)
So that is how it worked out for me. Obviously, if you have a puzzle card idea you won’t be able to use this as a how-to. At the time of writing, they have a job opening for what appears to be a full-time puzzle designer. As for a single card or two in a freelance capacity, you might be able to contact Mind Candy and/or Adrian to inquire about that sort of thing. I won’t be passing along the email addresses of Mind Candy people without prior consent, but if you’re a good ARGer, you can probably locate all sorts of email addresses without my help.