hetanavi (http://hetanavi.sakura.ne.jp/) is a great resource. It's a database of a ton of APH fansites. You need to know a little bit of Japanese, though- but just knowing katakana, doing some trial-and-error, and/or muddling around with the help of Google Translator will get you there in the end. You check off イラスト (illustrations) in the first blue section and the name of a country in the キャラクター (character) area and hit the grey search button at the top. Voilà. You can waste a LOT of time poking around the fansites, though- just a warning!

I'm with moriyama_umi in that I would only use official illustrations for icons (if I had space for extra icons). If I were to use fanart for icons, it seems proper to me to ask the artists for permission- no matter what language they speak. Just common courtesy, y'know? But I realize a lot of other people don't feel this way- I think I'm the only person who gets irritated by icon posts that don't credit the artist. ^_^;