Wemoto, or a friendly bike shop (if you can find one). otherwise take your chance on ebay.
do you put a cover over your bike when parked? if so its like a sail, a wind trap.
seriously, Wemoto for the mirror, but gear lever will be oem, (original equipment manufacturer) so Honda parts or ebay might have both bits. see if there is a breaker breaking one and ask if they have both parts, to combine postage.