Sure. Try here http://www.yourwdwstore.net/MagicBands_c_758.html or ebay, just be sure you read the descriptions for one that is link it later or link able. Some listings are for collectors items that you won't be able to actually use.
We aren't going until July but we knew someone who went in February. I asked them before they left if it might be possible for them to pick up the bands for us. They were more than happy to oblige and we now have our bands linked and ready to go!!
There are basic ones available online. However - Downtown Disney has an out of the park magic band location, and they do have many of the specialty magicbands. I was able to purchase my band there the night before and then use MDE to link them to my tickets.
IMO, Disney is missing the boat here. Disney should give you option to upgrade your band to a special band for a charge right on the site where you customize your band. Disney could then just ship you the special upgraded band. Disney saves money because they don't have to send you the first "free" band. You don't have to deal with the hassle of adding the new upgraded band once you get there. Everyone wins.