If you end up having to replace the headset to solve the problem, the only non-standard 26tpi pieces are the upper threaded race and the locknut. So you could replace just the lower stack (crown race and lower pressed race), which is what carries the load anyway, and keep the upper stack (upper pressed race and threaded race) and locknut from your old headset, since the upper bearing merely holds the fork in alignment, not carrying any of the load.