Best known method for siderophores production is :Schwyn, B., Neilands, J.B., 1987. Universal chemical assay for the detection and determination of siderophores. Analytical Biochemisty 160(1): 47-56.
Prepare CAS dye and mix with any minimal media with agar and without iron source. The solution should contain 8 parts of media with 2 parts of CAS dye.