there is a slipway in rosroe that is not private as far as i know,there is a very steep hill on the way in to rosroe,make sure the brakes are working on the trailer
you could ring killary cruises
http://www.killarycruises.com/ or scuba dive west
http://www.scubadivewest.com/ they have slipways that they might let you use or know of one you could use
there is a slipway across from the one the lads showed you not sure if it is private or not