If you want to fabricate your own from some 6061 angle, I have a cardboard pattern around that I could scan and post or mail to you. They are easy to make.
(I even have a fully-completed one in mirror-image of what it's supposed to be that I fabricated in a somewhat dyslexic moment 
)
There is a Hayes-made adapter for 22mm to 51mm IS. I found one at The Fix in Boulder, CO for $30:
http://www.thefixbikes.com/bikes/dept.asp?dept_id=3023
A2Z makes them as well. Part no. is AD-PMR. See here:
http://www.a2zcomponents.com/adapter/others.asp