once in a purple moon
seldom or ever
seldomly
once in a blue moon
unoften
seldom
in a pig's eye
rare
barely
rarely
superrare
impossible
inconceivable
out of the question
unimaginable
sporadical
nary
elusive
not hardly
uncommonly
at latter Lammas
at no time
if pigs had wings
when pigs fly
I can't remember the last time
rare as a four-leaf clover
infrequently
scarce
scarcely
hardly
by no means
not by a blame sight
not by a long sight
rare as rocking horse shit
not by any means
not while pussy's a cat
nevah
never ever
when two Sundays meet
when two Sundays come together
improbable
one in a million
scantly
unoccasional
rocking horse shit
geason
one man and his dog
not for the world
doubtful
rarer than hens' teeth