How to restrict the certain value in the value set for some set of users?

We have requirement , where we want to give EBS access to external user for performing material transaction but we want these user to transact only for certain locators not for all? we have associated value sets to each segment of locator, we want the only certain values(Like locators starting with 'MO%' to be available to external users , what are the options available to configure the same? Note client is using EBS 12.2.4 version