As Billyboyo, halfteck, mongan, and I'm sure others will say, your idea of scanning JCL is half baked, to say the least. Dataset names in JCL are often hidden in various ways, such as in procedures called from JCL and symbolic parameters. Just finding the JCL is enormously difficult! Dataset names are not always present in JCL in any event!
Your only viable option is to analyze SMF data. I grant this is difficult, but it is much less difficult and much more complete than trying to analyze JCL.