Although SZD had many sailplanes that where produced for purpose of
experiment or to accomplish/reach some target (which they never failed
not to); there never was a 2 place Jantar maybe someone was referring
to SZD-40 Halny which had a somewhat similar Jantar look, was built in
1972 and L/D of 43. There was only ONE built, so I don't know how
would it find its way to US. Here is a pic. -
http://www.piotrp.de/SZYBOWCE/pszd40.htm

And here are all the gliders built by SZD, before WWII and after:

http://www.piotrp.de/SZYBOWCE/pszd.htm