Change Zip Code Radius Search in Wordpress

We have a zip code radius in place that works but we want it changed to operate differently. - It currently searches for a management company/vendor in cities within 50 of the zip code you enter - See Attachment "Zip-Search" - Currently on the Back-end (WP-ADMIN) we Select the state and/or city that the Management Company/Vendor is assigned to - See Attachment "MGT-BACKEND" - We do have an option in the backend to add multiple zip codes but it is not used. - See Attachment "Multiple-zips" - When You add multiple zip codes in the back end it create a DB field for post_zip - See Attachment "zip-db-1" - We have a zip code database with Lat/Long already in place and have been using it (IT WORKS ALREADY) - See Attachement "zip-db-2" OK. So here is what we want it to do. When someone does a search for a zip code (ie. 90210) it needs to look through the post_zip in the DB and see if any zip codes are within 50 miles of that zip and display Management Companies/Vendors within that proximity. Not searching for CITIES within 50 miles but ZIP CODES (I have found where it is doing this in the code for easy reference) We need to be able to assign as many zip codes as we want in the back-end. (in Attachment "Multiple-zips") The Code is already there and just needs altering to make it work differently. Should be a quick easy job for fast money for a GOOD Developer.