A friend who posts regularly here clued me in to the treasure trove of inexpensive lossless downloads available from Supraphon at
http://www.supraphonline.cz/ (nice portmanteau). Start to type Smeta... into the search box and you will see a link to "Smetanovo kvarteto" (=Smetana Quartet), which includes many splendid recordings that have never appeared on CD, as well as some that have but are now op. Mono FLACs cost the equivalent of about US$3.50 per album, and stereo about $5.25. No registration is necessary if you permit a link to Google+, and credit card payment is at a secure third-party site. I purchased the Dvorak op. 34 / Martinu SQ#4 coupling, the early '50s Smetana SQs, the '50s coupling of Dvorak op. 105 / Mozart K. 465 (not the same as the '60s EMI recordings reissued by Testament), and the Prokofiev #1 / Shostakovich #3 pairing. Transfers sound splendid, and the excellence of the performances probably is well known to anyone who has read this far.
Oddly enough, the 1962 recording of Smetana's SQ#2 still seems to be MIA; I don't think it has ever appeared on CD (the listing in Youngrok Lee's discography is incorrect iirc) and wonder why not. But there is a 1985 live recording of the piece c/w Beethoven op. 131 and a work by Kalabis that I do not recall having seen before.
Poking around the site. I found many desirable recordings by other artists. An odd paucity of Janacek SQ recordings (only the DG box!), and I was disappointed to find only one Plocek/Palenicek recording (Mozart Sonatas, but no Beethoven, and none of the old Czech Trio recordings w/Sadlo). But it's silly to dwell on what is not there when so many wonderful recordings have been made available for a reasonable price.
Downloading is slow but trouble-free, and the site keeps a record of purchases and allows multiple downloads. The zip files come with FLACs (or mp3s if you prefer--they're even cheaper), an image of the front cover, and an option to download PDFs of a jewel case insert and a sheet with recording information. Everything is in Czech, but easy to decipher with minimal assistance from Google translate.
AC