Synonyms for Now and then:

adv.

infrequently (adverb)
infrequently.
once in a while (adverb)
infrequently, on occasion, now and again, occasionally, at times, once in a while, from time to time.

n.

infrequently, seldom. now and then (noun)
from time to time, once in a while, now and again, on occasion, occasionally, at times.

Other synonyms:

at times
at times.
now and again
now and again.
seldom
infrequently.
Other relevant words:
occasionally, seldom, infrequently.