Search the archives this was discussed previously and there are no easily available solutions. I've seen some that mount to the frame downtubes and some that mount to the head, neither of which is a good position (head mounts can damage your head if you hit hard). Actually I found the source for the downtubes ones which are probably the better solution anyways. It is in Danish but I understand people have ordered these before to the US: http://www.sports-mc.dk/index.php?t=select&l=dk&v=dkk&mpg=3&mk=4&mo=689&yf=1988&yt=1991
They've got them for all the cradle-frame GSXRs. And that price 1039 DKK works out to about $125.