Nowhere. They were given out as part of special programs...either special groups or events.
I have never seen them for sale anywhere...at least not like the ones that I have.
To just prove that you can teach an old dog new tricks, there it is. Not really 3D (kind of deceiving that) but enhanced. Cool! Might see if I can try that sometime. I'm going next week! Where can they be purchased? How much?
I've seen them at Cracker Barrel at Christmas time for $1.99 a pair (in fact I have a couple pairs), but I don't know if there's any place that sells them this time of year.