Welcome to the forum, from sunny california
I am not familier with the Ultra Legacy, Have you tried contacting Ultra Cycles for parts?
http://www.ultracycles.com/
or
maybe you could take the measurements from the old shock, I am assuming you have at least one shock, and try to match it up to one at your local cycle shop? You may have to go around and measure several other bikes to find one that is close to yours.
Measure mounting bolts upper to lower, center to center. measure the length in the bikes lowest bottomed out position, and the highest position, I am guessing the travel is approx 3" to 4" or so. get the diameter of each bolt. get the outside diameter of the shock you have, to make sure you get one close, you dont want it to rub on the fender etc.
hope this helps.
EDIT:
I just looked closer at the Ultra Cycles website. They dont show shocks, but if you send them your vin number, maybe that is how you can get the correct shocks.
shocks 
Linear Mode
