you do not have to mix them before spraying. you could spray Zinc sulfate solution first and then Fulvic acid. Fulvic acid dissolve very well in water at high pH values.
I am giving you just one sugestion that spray of macro and micro chemical fertilizers higher concentrations adversely affect on crop plants so please use a minute quantity for spray and experimently in small scale may be 0.1 or 0.2% than can be used increased concentrations.