The Collaborative International Dictionary of English v.0.48:

Unwarned \Unwarned\
   See warned.

Moby Thesaurus II by Grady Ward, 1.0:

32 Moby Thesaurus words for "unwarned":
   bare-handed, defenseless, guardless, helpless, inexpectant,
   nonexpectant, unadmonished, unadvised, unanticipating,
   unanticipative, unarmed, unarmored, unattended, unaware, uncovered,
   undefended, unexpecting, unforewarned, unfortified, ungarrisoned,
   unguarded, unguessing, uninformed, unprepared, unprotected,
   unready, unscreened, unsheltered, unshielded, unsuspecting,
   unwatched, weaponless