Search for users near a location

I've been looking at the core and advanced search options for community builder. Is there a known way to modify the code to allow searching near a location, i.e. you want to find members within 50 miles of you?

CB Advanced Search looks great but didn't appear to have that functionality.

CB does not offer such a search feature, sorry. You'd need a 3rd party plugin or extension to expand userlists or add a new fieldtype which allows such searching. Recommend checking Joomla.org extensions directory.