Martin
It is not clear from your post if you are looking for a spare to modify or you do not have a fixed steady at all. The lathe when supplied should have had a fixed steady with it. In any event , a first point of call should be Warco themselves.
I should be a simple job to make new fingers for the steady and incorporate a small ball or roller race. Ideally this race should be supported on either side by the new fingers,i.e. forked ends. If the loading is light you could get away with fixing the race to one side of the finger.