It's quite common... there are a number of regular gaijin (been there for years and years), in addition to those who visit for a few months..
You might like to take a look at 'The Empty Mind' clips on the Aikikai Hombu Dojo at youtube
- just search for 'empty mind'. There are lots of keiko scenes and they interview a 'gaijin' at the beginning of the segment on the Aikikai
BTW, I have the Empty Mind DVD and it's really well done.. highly recommended