Yeah, neither of those solutions are ideal, which is why I suggested the most simple of options which is moving this thread to the Sandbox forum. All members, premium and non-premium can access that forum, but non-members (guests, google search, etc.) cannot.
The other solution, a little more secure still, would be a private thread where the thread starter would have control over who is allowed to see the contents of the thread. That's not a feature supported by the regular board software that I know of and would require a plugin or patch of some kind. That's work that Dave would have to do, so I'm not expecting him to take time implementing it.
At the end of the day the only problem was people calling Sideshow's phone line about codes. I can absolutely see that as problem and as a business owner myself I would find it tedious to deal with if it got out of hand. However, I believe something like this would happen or could happen even with strictly legitimate codes, after all, most of them expired after 10 minutes. My other concern with regards to search and guest access to this thread is that Sideshow may continue to receive calls about codes when someone finds them posted months from now. "Hey Sideshow, I just found a few codes on a forum and I can't figure out where to type them - or they're not saving to my wallet - what's going on?"
There's only so much one can do to idiot-proof a public space. I think moving the thread into the Sandbox forum is the easiest and least impactful alternative.
I've echoed my sentiment on these promotions many times before including the reward points system and giveaways. I believe they are a huge boost to Sideshow's sales both during the promotional period and well into the future. A few dollars of discount here and there will make the difference between someone buying or skipping a release. I also feel that this thread, in particular, drives a significant amount of traffic to Sideshow's site and social feeds, plus drives a significant amount of sales to their store.
Thank you again Sideshow!