rarely
infrequent
uncommonly
infrequently
seldom
unoccasional
nonfrequent
unfrequent
occasional
once in a blue moon
stated
seldom or ever
I can't remember the last time
off and on
on and off
occasionally
episodicity
on occasion
from time to time
now and then
casual
at times
once in a while
now and again
seldomly
episodic
sporadical
unoften
sometimes
sporadically
nonprevalent
opportunity seldom knocks twice
unprevalent
periodically
patchy
accidental
nonsporadic
discontinuously
nonrecurring
oft
adventitiously
once in a purple moon
frequent
semiperiodic
unregular
as often as not
eternally
noncontinuable
unexpedited
unperiodic