So it looks like the beer gods have shined on me - I've landed several 1/4 and 1/6 barrel Sanke kegs to add into my collection. This is more just informational, but once you take out the retaining spring, all you need to quickly put a Sankey keg into use is McMaster #99142A590 and a cheap pair of retaining-ring pliers. I chose McMaster #57805A361.