Paulo,
Welcome!
www.ktmtwins.com is a good all around place to get things, but I usually look on this forum, see what people like, then google it and do an ebay search to find a better deal on the most expensive parts. If you want to look at KTM models and parts that aren't available in the US, this is a good site:
http://www.ktm-versand.de/index.php/lan ... 7dbddce67c . I bought my white body kit from them a few years ago.
The factory mirrors may not look stylish but they work well. I still haven't found a substitute that will look good and work as well as the stock mirrors, so I'm still using them. On my old Monster I had a beautiful looking set of Rizoma mirrors, but they were useless, and once I got this bike, I decided I was never going to deal with having poorly functioning mirrors again.
Judging by your name, you must've had a 749? What year? The bike that got me liking motorcycles was a 2005 749R my friend owned... it looked and sounded amazing! The $1200 valve adjustment it needed wasn't too nice, but every bike seems to have some kind of glitch.