the only system table is msdb..sysdtspackages. however it's binary format.
there is a vbscript out there which will interate through that table and save the packages as structured stored files or vbscript files which are text files. then you can search through thoses with some basic file IO routines.
I'ts been a long time since I saw that vbscript file but I'm sure you can find it via google.