Hi Mau,
You may filter the Content Center Library by Standard Organization. I note that a filter for the British Standards Institute (BSI) exists.
Please note the OTHER standard content center library should be installed and included in the active project. The OTHER library contains much of the BSI content.
Have you searched the content center with this filter enabled? What type of content are you looking for?
There are also several free online part libraries that may be helpful.
http://www.3dmodelspace.com/autodesk
http://autodesk.partcommunity.com/portal/portal/autodesk/PARTcommunity/Portal/autodesk
http://grabcad.com/
http://www.tracepartsonline.net/(S(np15mqndwemvot45hkiohdmo))/content.aspx?ClsID=/ROOT/C21/C21.060/C...
McMaster-Carr is a great online retailer that offers CAD models for a bunch of items.
http://www.mcmaster.com/#standard-cap-screws/=p8z3ez
Finally, you can create you own custom content center libraries if you do not find exactly what you are looking for. I hope this helps.
Let me know if you have any further questions.
Cheers,
Nathan Chandler
Principal Specialist