The Collaborative International Dictionary of English v.0.48:

Attainable \At*tain"a*ble\, a.
   1. Capable of being attained or reached by efforts of the
      mind or body; capable of being compassed or accomplished
      by efforts directed to the object.
      [1913 Webster]

            The highest pitch of perfection attainable in this
            life.                                 --Addison.
      [1913 Webster]

   2. Obtainable. [Obs.]
      [1913 Webster]

            General Howe would not permit the purchase of those
            articles [clothes and blankets] in Philadelphia, and
            they were not attainable in the country. --Marshall.
      [1913 Webster]

WordNet (r) 3.0 (2006):

attainable
    adj 1: capable of being attained or accomplished; "choose an
           attainable goal"; "art is not something that is come-at-
           able by dint of study" [syn: attainable, come-at-
           able]

Moby Thesaurus II by Grady Ward, 1.0:

33 Moby Thesaurus words for "attainable":
   accessible, achievable, actable, approachable, available,
   come-at-able, compassable, doable, feasible, findable, getatable,
   gettable, negotiable, obtainable, open, open to, operable,
   overcomable, penetrable, performable, pervious, practicable,
   practical, procurable, reachable, realizable, securable, superable,
   surmountable, to be had, viable, within reach, workable