Database of polycyclic and hetrocyclic compounds

 Hi CCLers,
 	For all those chemists (particulay organic
 chemists) out there, please forgive in advance
 but please read on!!!!!
 	I am trying to find a database that lists
 atleast all the possible polycyclic/hetrocyclic
 compounds upto about 12 rings and hetroatoms of
 oxygen, sulphur and nitrogen.  Of these hetroatoms,
 the most important is oxygen as I guess the
 number of permutations will become large with
 sulphur included.
 I have looked in our library and am a little
 daunted by the 50+ volumes of possible compounds
 with no apparent global index or heirachy - I am
 hoping a computer database exists or a good
 hardcopy index with some sort of listing that
 starts at 1 ring and no heteroatoms and goes down
 from there (i.e. something that has done the sorting
 for a non-organic chemist).
 Please send requests to me at m.biggs $#at#$
 and I shall summarize.
 Many thanks
 Mark Biggs
 Dept of Chem and Process Eng
 Surrey University, UK
 PS: This is linked to computational chemistry!