The Collaborative International Dictionary of English v.0.48:

Unimagined \Unimagined\
   See imagined.

WordNet (r) 3.0 (2006):

unimagined
    adj 1: not imagined even in a dream [syn: undreamed,
           undreamed of, undreamt, undreamt of, unimagined]

Moby Thesaurus II by Grady Ward, 1.0:

70 Moby Thesaurus words for "unimagined":
   authentic, bona fide, candid, card-carrying, dinkum,
   following the letter, genuine, good, honest, honest-to-God,
   imageless, inartificial, lawful, legitimate, lifelike, literal,
   natural, naturalistic, original, pure, real, realistic, rightful,
   simon-pure, simple, sincere, sterling, sure-enough, true to life,
   true to nature, true to reality, unadulterated, unaffected,
   unassumed, unassuming, uncolored, unconceived, unconceptualized,
   unconcocted, unconsidered, uncopied, uncounterfeited, undisguised,
   undisguising, undistorted, undreamed-of, unexaggerated,
   unfabricated, unfanciful, unfeigned, unfeigning, unfictitious,
   unflattering, unimaged, unimitated, uninvented, unpretended,
   unpretending, unqualified, unromantic, unsimulated, unspecious,
   unsynthetic, unthought-of, unvarnished, verbal, verbatim,
   veridical, verisimilar, word-for-word