rarer than hens' teeth
superrare
geason
rareish
rare
semirare
rare as a four-leaf clover
ultrarare
attenuate
rare as rocking horse shit
one in a million
uncommon
ultrararefied
rocking horse shit
historically
rarefactional
nonrare
few and far between
rare as hen's teeth
rareness
remarkable
seldomly
sporadic
seldomness
rarefiable
rarefication
sporadical
unoften
once in a blue moon
rarity
unique
dead donkey
antrin
seldom
rarely
unmiraculous
sporadicalness
supersubtle
scarce
unusual
uncommonly
uncommonness
unrarefied
nonrarefied
out of the common
rarissima
not grow on trees
once in a purple moon
elusive
different