The OED has nothing; THE NEW YORK TIMES EVERYDAT DICTIONARY OF MISUNDERSTOOD, MISUSED, AND MISPRONOUNCED WORDS has nothing; MRS. BYRNE'S DICTIONARY has "pinacotheca" [note spelling] as "a picture gallery"; ROGET'S INTERNATIONAL THESAURUS lists pinakotheke and pinacotheca in group "museum . . . picture gallery."
I was going to promote the article "Words Weird and Wonderful" in Wolfe's CASTLE OF THE OTTER (collected in Wolfe's CASTLE OF DAYS), but it doesn't have that word in it. I promote it anyway! (LEXICON URTHUS only says it is a picture gallery, fwiw.)
There used to be an online wordlist of New Sun words, probably more than one iirc. Another resource.
=mantis=
Sirius Fiction
booklets on Gene Wolfe, John Crowley
hurt books eBay auction coming soon
http://www.siriusfiction.com/