I haven't actually been to London in ages but loads of people were sending me postcards from where they lived and I couldn't find any in Southampton! So I decided I'd look online instead, and look what I found!
They had loads of postcards on sale at http://www.clicksouvenirs.com/ so I bought loads! They have loads of cheap British souvenirs, it's great!
Look forward to a postcard in your letters soon!