Through bars end covers are available separately:
Left hand side (single, excluding locks):
https://www.roofbox.co.uk/scripts/rbvehsel4_tab.php?QPR25-02-202A (Whispbar branded)
https://www.roofbox.co.uk/scripts/rbvehsel4_tab.php?QYK25-02-202A (Yakima branded)
Right hand side (single, excluding locks):
https://www.roofbox.co.uk/scripts/rbvehsel4_tab.php?QPR25-02-203A (Whispbar branded)
https://www.roofbox.co.uk/scripts/rbvehsel4_tab.php?QYK25-02-203A (Yakima branded)
Lock barrels are also available separately if you need one:
https://www.roofbox.co.uk/scripts/rbvehsel4.php?query=QPR8871xxx