I use a 6D right now and that's why I'm unsatisfied and want a bigger one. I have no problems with its size and don't think I'd mind carrying something more. I carry it with me through nighttime hikes in the woods and wouldn't want it for mountaineering but for short walks of under a couple miles or so, it's quite useful. I didn't realize they're so expensive to make...maybe with everyone here interested in buying one, we could do a group purchase somehow?
And bears are one reason but not the primary reason, something to deter or possibly protect against predators of the two legged variety is very useful as well in jurisdictions where almost anything else is illegal to have. Not to mention having longer battery life simply due to more of them. And the undeniable cool factor of having such a light can't be ignored either.
I didn't think to check with local machine shops, but I wouldn't know what to ask for. Just telling them, "I need a replacement tube for a Maglite to convert it to a 12D", they probably wouldn't know what to do. I wouldn't know what specs to give them, either, so I was hoping there'd be people here that are experts in both flashlights and machining. One of my friends was a machinist for years and I'm sure has the skills but not access to the tools and equipment anymore.