(WARNING *** IF I DON'T ANSWER, IT IS BECAUSE I SEEM NOT TO KNOW HOW TO GET NOTIFICATIONS FOR MY OWN POSTS - HOPE TO RECTIFY THIS SOON)
I went the DIY route with NANUK (Like Pelican) cases on a GIVI Rack. I used the T-Slot materials from Lee Valley and so far I have things relatively worked out. But I need a locking mechanism.
At present, drilled a hole across the track and installed a machine screw with nylon locking nut to prevent the cases from sliding out the back. And for the top I drilled a hole across the track and dropped a machine screw to act as a clevis pin to prevent them from sliding out the front.
But I am looking for a thin diameter shaft lock - much like the trailer ball pin locks. Something less than 1/4"
Are you looking for a lock for the pannier lids or locking the pannier to the bike?
If its the lids go to the hardware store and by a few keyed small pad locks and use the existing lock holes already cast into the cases. When not in use clip the lock to a hole in the handle of the case.
One lock per side is all I ever used and yes you could still pry open the non locked side a bit but the reality is the cases are plastic and locks only keep honest people honest.
If you looking to lock the panniers to the pannier racks, just bolt then on. If you're worried about losing the "quick release" option don't worry its something you'll rarely use.