Please, need help.

For a long time now I am searching for an external directional antenna
for my wl-300g. Something like you can find here: http://www.multimediacenter.nl/websh...=90-IAEAN1000- . Where can I order (e.g. in Germany) this antenna. Or at least an 'optional connection adapter RP-SMA' as mentioned so many times on the Asus Product pages (see http://de.asus.com/products.aspx?l1=...94&modelmenu=1 ).

Your help will be appreciated.