That Convair Space Shuttle kit was reissued by Revell-Monogram about 8, maybe 10 years ago, so it might still be available at either eBay, at one of the older, well stocked model shops that do mail-order, or from one of the kit dealers who advertise in Fine Scale Modeler . It's still a nice kit after so many years.
The XSL01 Moon Rocket is now a very rare kit that goes for Big Bucks. I built one in either '58 or '59 and only saw it on my local hobby shop shelf one time (and a little later the issue of the separate first stage delta rocketplane pictured here, moulded in a light blue plastic as compared to silver in the full version). It's never been reisssued, unfortunately. But it _was_ considered by Revell-Monogram! At one of the IPMS National Comventions in the mid-90s, I had the opportunity to ask one of the Revell-Momgram VPs if they would ever reissue that kit (as part of their golden-oldies reissue program). I asked the right guy, it turned out, as he had personally inspected that kit's molds and though in good condition, the clear-parts die was missing. He said that would probably keep it from ever being reissued.
I bought a MIB collectors copy of the XSL01 about 10 years ago and it cost $400, a very good price at the time, considering its price range listed for it in the Burns Kit Collector's Guide. It was worth it to me to be able to recapture a cherished memory from childhood--but's it's too rare and valuable a kit to ever build now.
A piece of science fiction TV trivia rearding this old spaceship kit: If you remember the "Men Into Space" syndicated TV series from that early space era, well, in one episodes, the XSL01 was used as a Russian Mars ship that was to be lauched from the Russians Moonbase until--if memory serves--a Moonquakre destoyed it.
--Ken