When both clips broke within a week on my Timbuk2 messenger bag, I knew I had to do something. This coincided with me fixing my 3d printer (it was the extruder feed: it was too loose all along!), so I was able to prototype a new clip.
The files are on Thingiverse: Messenger Bag Replacement 25 mm Webbing Clip, or there’s a local copy here: Messenger_Bag_Replacement_25_mm_Webbing_Clip.zip.