There are several directories that contain lists of production services compani
es including special effects houses.  A directory that happens to be close to h
and is THE PRODUCER'S MASTERGUIDE (Shmuel [sic] Bension).  I have the 1988 edit
ion; there may be later ones, I know there were earlier editions.  This particu
lar directory is worth knowing about since it includes a wide range of informat
ion that one should know (or know about) such as union and guild contract terms
, film commissions in various jurisdictions, and a useful summary of the
business of feature film production.