You can easily add new manufacturer and catalog items to database in AutoCAD Electrical. If there are more (hundreds of..) products I recommend to use MSAccess or other software which can read *mdb format. You can convert the tables to Excel format and fill the information and convert back to MSAccess.
Add the new components as you use them in your drawing (assuming you know the required cat/man information).
Other than that, you can always ask your supliers for a database in excel format and import that into the catalogue file using MS Access
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