how to search for a single address (field) in two different records

We have a custom record that contains multiple location addresses for a customer. We have to use a custom record for this data because we can't add additional fields to the delivered address record on the customer.

We are, however, using the delivered customer address record for billing address.

What I need is the ability to search BOTH records for a specific address (e.g. 123 Main Street), entering the address one time, and return the results to be viewed or selected.

How can I setup a search form to look into both records? I understand that NetSuite OOTB only allows searching a single record (i.e. no unions). My thought is to create a custom form (based on another custom record?) with a custom 'Search' button. Through script, the search would pull from both the delivered customer address record and the custom location address record and display the results.