You can create an Odoo Server Action that uses the "as the crow flies" distance.

This relies on the Partners Geolocation module, so be sure to install it before trying, and to geolocate / geocode all of your Customers:

The Server Action would be set on the sale.order model and have code similar to this:

Access sample code here

Once finished, click Create Contextual Action so that your Server Action appears in the Action Menu on each Sales Order:

Sample Search:

Note: This is a rapidly generated proof of concept - it also searches all Contacts - you would need to narrow down the search based on how you classify your Contractors. Contact your Odoo Digital Advisor or your Odoo Partner for further help converting this into a solution suitable for a production database.