I also wear a size 22.5 and I've tried on just about everything out there. I finally found my boot, but it cost a pretty penny, Nordica's Dobermann WC 100, it's plenty stiff (way stiffer than everything else I tried, nordica boots tend to be stiff) but it's a 95 lasting, so if you don't also have a really narrow foot it might not work for you (I needed to have the forefoot punched). In so far as the sort of performance flex and size you're going to want to look at high end race boots, both atomic (redster) and technica (inferno) carry 22.5 boots in their high performance race line up, I'd look at those or the dobermann. In my experience even the women's "performance" boots are soft pieces of shit, which is I why I encourage you to look at the unisex race boots. Costly, but worth it if you can get a perfect fit.
You might get lucky and have a shop willing to work with you some. My local shop was willing to order a couple 22.5's in models that they didn't normally stock with no obligation on my part to buy, depending on their relationship with the given manufacturer. They couldn't get the dobermanns for me though, those I had to order through a vermont ski shop, which was the only online retailer that I could get them through, at least in a 22.5. Like most online shops they had a resonable return policy, fit the bill for shipping, and don't wear them on the slopes, you can return for a full refund within 30 days. I live in a pretty big ski town and I still had to do things this way, you might have better luck in mammoth, but if not, online is your best bet.