User Access

Hello All. I am in need of some help.

I have this application that I designed to monitor closings. I am looking to let remote parties log on and add closings to the schedule. I am able to do that fine. But when they go to add their closings they use a lookup field from my inventory. The inventory has 6 fields ID, Address, State, CAID, CA, CLNA. The CAID is the identifier of the Closer. In the users table I have USERID, USER, PASSWORD, EMAIL, GROUP
When I add a external user I put the CAID that corresponds to that USER. When they log on they can go to the Closings Table and see only the inventory that has their CAID. That works fine.

When they add a closing and put id the ID from the inventory table it autofills that property. Is there a way that when they enter a ID it will only bring up property ID's that are assigned to them in the inventory table.
I hope that I explained this correctly.