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