I love these old recorders! I have several and they are totally impractical, just like all my other stuff! As I sit here in my living room watching black-and-white TV on a 10-inch screen, making records on a Recordio seems like a perfectly normal thing to want to do!
Discs are still available from a couple of places, including the same source I was buying them from decades ago when we were still custom cutting 78s commercially:
Transco. Coincidentally, Transco is located just down the road from me.
NOS blanks will work (as will, apparently, certain disposable plastic dinner plates!) but usually won't offer the best results. The acetate coating dries out over the years and become harder which makes it more difficult to cut, and results in a noisier recording. New blanks are still optimally soft and cut as cleanly as possible. Of course, the Recordio and other home "cold cutter" units didn't make all that great sounding recordings even when they were new, compared to the professional cutters.
I've run across information out there on the web (sorry, I couldn't find it just now) about how to convert a cold cutter to a hot cutter. I haven't tried it, but the people who have say it's not difficult, just a turn or two of nichrome wire around the stylus. It's apparently a little tricky setting it so the heat is enough to make the lacquer cut like butter, but not hot enough to ruin the stylus! Adding a vacuum system to collect the thread (be sure to do this the right way, 'cause that thread is extremely flammable!) is another relatively easy mod that can make a home unit work a little more like a pro model.
By all means, pick up these units (as long as they're not overpriced) and keep them running. Or pass them on to another wacky collector who will.
--Dave