You may be able to find some data from the major photographer organizations like ASMP, NPPA, PPA, EP and the like. Or photo schools like Art Center, Brooks and RIT. They will have statistics on the numbers of students and alumni associated with their schools.
If the feds don't have the data base on those ratios, then you will have to use the data from the above professional organizations and then do a SWAG and go from there.