I definitely agree that the game could use, and deserves more exposure than it has. What do you think would be good places to try and get it mentioned at? It has a small roguebasin article, it's mentioned at thelist.roguelikedevelopment.org (althought the version listed there is a really old one) and as you said, there is some information on it at roguetemple. I *think* Nahjor posted about it at rgrd as well. Maybe requesting a full interview from Slash at roguetemple would be a good plan? Would it be appropriate to try places like the the oook and ToME forums' off topic sections?
As for finding the site, it's easy to get here from glistenimages.com, and google searching Lukos Software gives it as the first result as well. Googling for "Mage Guild" is a lost cause, unless this game can somehow surpass The Elder Scrolls series in popularity, which is currently the top result for that. Of course, if Nahjor was able to pull that off he wouldn't need any more advertising.
It really is the best roguelike I've seen in a while though, and that the only reason it isn't more popular is because people don't know it exists.