those are pretty easy to find, Heck I just sold a bike and threw in 8 of the yaun ta internal brake ones so he could mix and match hubs/wheel bands to make a couple of perfect ones for the restoration of the bike.
There are some NOS sets still popping up for sale on ebay from time to time as well, they are "san remo" Brand, internal brake and were used on a variety of bikes in the 70's. Lots of used one to be had as well:thumbsup: