Hi Bert,
Presumably, you have approximate coordinates for the object.
Go to the SIMBAD database and search by coordinates (Coordinate Query).
http://simbad.u-strasbg.fr/simbad/sim-fcoo
You might want to broaden the search radius to say 2 degrees. Then sort the objects by type (select an arrow under Otype). The PNs should all group together. Will probably have all the NGC and IC PNs but not sure how all-inclusive the database is.
Regards, Rob