You can use chemically define agar medium contains glycerol as carbon source and followed by  soil samples serial dilution technique. After incubation at 25 to 28 deg. you can isolate actinomycetes culture.

 In secondary screening  chemically define agar medium contains x-gal , so during growth the colony which give blue colour during growth can be consider beta galactosidase producing actinomycetes.  Further the Beta-galactosidase assay can be use for quantitation of yield .