I have mirrors on both my ski's and IMO they are 99% useless, I do occasionally check to see if my ride buddy is behind me, but usually I just look over my shoulder, especially if making any kind of turn, the mirrors only offer a tiny view of what's actually behind you so if your going to change direction, its critical to do a solid visual sweep behind you just in case your buddy or some bass boat was hauling ass and was about to pass.
I do a lot of river runs where I need to constantly check if the guy behind me is still there due to the danger's involved and the number of twists and turns, on my last 30 mile run down the peace river (just two of us out there) I probably checked for him at least 30 if if not 40 times, I'll glance into the mirror and if I don't see him i'll look over my shoulder and slow down to let him catch up, It was important to know the he hadn't somehow ended up face first into the trees on a bad turn, my quick reaction might be the difference if I need to help somehow.
if it was me, i'd skip the mirrors, but if your determined to get them, then you can find them cheap and easy on ebay, and could just spray paint them the color you want if you can't find a perfect choice, The older ones for 2 strokes are usually $10-$15 + a few dollars shipping, they usually remove pretty easily (but ya sometimes the nut spins and on those I just give up because the mirrors are like $7 profit for me after shipping/fee's so I don't care too much)
edit: one friend i know with a blaster installed a bicycle/motorcycle style handlebar mount with a $7 mirror on it, it looks goofy but serves it purpose.