Your initial structure is fine, you just need a couple more tables to make the relationships between the Occupation - > Location table and the Employer -> occupation table.
I could be wrong, but it seams to me that an occupation should be allowed to relate to multiple locations; Harry the plumber may be willing to work in location 1, location 4 and location 5.
so create a linking table to create these relations:
occupationlocations:
occupationlocationID - primary key
occupationlocationOcupation ID - Foreign key to Occupation Table Occupation ID
occupationlocationLocationID - Foreign key to Job Location Table Location ID
Now for the link to locations and occupations tables from the Company table. I could be wrong again, but it seams that company a might be interested in plumbers from location 1, but not electricians, they may want electricians from location 2.
the linking table for Companies to Occupations and Locations would be:
employeroccupationlocations:
employeroccupationlocationsID - primary key
employeroccupationlocationsOLID - Foriegn key to occupationlocations.occupationlocationID
employeroccupationlocationsEmployerID - Foriegn key to Employer.EmployerID
