Are there other (eviormental, exposure) cause which can lead someone
to develop Neurofibromatosis other than being passed down via from
your parents?

No, because NF is defined as a set of genetic disorders which cause
tumors to grow along various types of nerves and, in addition, can
affect the development of non-nervous tissues such as bones and skin.

The definition of 'genetic disorders' means it can only be passed on
from your parents and their parents.

Tumors and Cancer can be influenced by enviromental factors though.

NF-1 and NF-2, the two commonly recognized forms of NF are both
autosomal dominant, genetically inherited disorders.  However, 50% of
people with either form do not have a parent with the gene - it is a
new mutation.  Further, some of those whose parents have the gene as
well, the parent has never been diagnosed, because the manifestation
may be very subtle for some individuals.  Thus in more than half the
cases of neurofibromatosis, neither parent has ever been diagnosed
with NF.  However, someone who was not born with the gene cannot
develop NF through environmental exposure.  The disease may not be
apparent at birth however, but only cause problems later on.