FatCat
Maester
Hmm, if it's a rebel-type organization you could always use the 'Sons of ____ '(insert countries name here), kinda classic counter-culture namesake imo. It's tough to find the perfect anything, but I'm sure if you keep taking swings at it something is bound to click. Is this a political movement/rivalry that the countries populous is privy to, or is it kind of a magical rivalry being fought behind the scenes? Also, you may be over-thinking the name and getting drawn into a somewhat trivial headache, names don't always have to reflect all the ideals/passions/philosophy of the group. Try going simple! For example Monarca doesn't immediately bring any specific purpose to mind other than transformation, which I'm guessing is the point. The counter to this could be something like the 'Stalwart Shadow', implying unseen resistance.