How many private, limited-circulation, special-interest newsletters of
one sort or another are currently being published in the United
States?

I am talking about little club newsletters, church and social group
and hobbyist newsletters, periodicals of professional organizations
and service populations and agency clients and investors and all kinds
of other groups and readerships--any kind of regular print publication
that is not a commercial magazine and that serves some definable
special category of reader or member.  I'm looking for an estimate of
how many such newsletters (not readers, not circulations, not
individual issues, but distinct, identifiable newsletters) there are
in the U.S.

I know an actual number would be impossible; for example, in American
Mensa alone, there are more than 120 local chapter newsletters, and I
doubt that that figure is in anyone's statistics outside Mensa. 
Still, has someone published an approximate number somewhere as a
guess at how many there are?  That is the number I am after before
midnight tonight (for a talk tomorrow--this is not homework!)--and
it's now 9:33 my time.

Thank you.
Apteryx-ga