You can usually find them at the Bazaar if you aren't lucky enough to get the drop yourself. I forget which level it is that they're most dominant at. I think they're somewhere between 15 and 20, maybe up to 25. That will at least help you narrow down your search so that you don't have to look at every item before you find what you're looking for.
Once you find a piece, look in the other categories at that level and you should find the rest, assuming the Bazaar has stock.
From various bosses around the Spiral. Few can also be located in the Bazaar. If you know what style you would like your clothes to come in, I can help you locate sources. Check out Eloise Merryweather's clothes that she sells in Wizard City (as these are the only styles that come with insignias), and let me know what you are interested in.
Where do I get robes, hats, and boots that have my own school insignias on it? It would be cool to have my own look.
~ 85
hmm. well you could get some from the bazzar. or. buy it in the crown shop. OR (lol). farm the guys in mirror lake. other then that. I can't think of any way else to get that kind of gear. I hope this helps.