To do this, you must first provide READ access to the Person's own company using
rule readCompany {
    description: "Allow Read Access to Person's Own Company"
    participant(p): "org.acme.shipping.participants.Person"
    operation: READ
    resource(comp): "org.acme.shipping.participants.Company"
    condition: (p.company.getIdentifier() == comp.getIdentifier())
    action: ALLOW
}
Then can grant access to all the containers to the persons belonging to company of type Border using your same rule as
rule border {
    description: "Allow Border access to containers"
    participant(p): "org.acme.shipping.participants.Person"
    operation: READ
    resource: "org.acme.shipping.assets.**"
    condition: (p.company.type == "BORDER")
    action: ALLOW
}