You can do this with an onLoad Catalog Client Script that uses GlideAjax to call a Script Include, passing in the reference table name as a parameter. The Client callable Script Include will simply query the table, pushing every record's sys_id to an array, then return the array comma-separated. Back in the Client Script, set the value of the List Collector variable to the value returned by the Script Include. Post your script attempts using the insert code icon </> if you get stuck, and we'll get it sorted.
