I haven't had to order any parts for mine, but I understand that they're easy to come by through BSA UK. Apparently the delivery time is within a week to the US and the customer service is supposed to be excellent.
Most of the major components on the bike are made by aftermarket companies, so those should be easy to come by as well.
I don't foresee parts being a huge problem, perhaps just a slight inconvenience.
But like I said, I haven't had to buy any yet...so whadda' I know.
Good luck with it if you get one. FYI, I have a nearly new '02 with less than 1000 miles on it that I'm selling. I'm in Atlanta.
E-mail me if you want to know more.
skyfroggy
AT gmail
DOT com