Yes, need a couple of these, these are horrendously expensive elsewhere. Almost better off buying another second hand keg.
All of the seal kits, lid seals, dip tube seals etc are also very expensive.
Yes these less popular fittings are really much more expensive. I would always suggest to anyone getting into kegs to go with the Cornelius type kegs as the parts are cheap and available. The quality of the second hand kegs has progressively been getting worse over the years. I would probably not even suggest getting second hand kegs at all and just go with new ones. We give 10 years warranty on the new ones that we sell and they are getting pretty close in price to the second hand ones.