It is a little difficult to find raclette in Basel as it is not very much in demand. I made a few calls and the only one is the Walliser Kanne. I called them, they said you can have it any time, make sure you make a reservation or I'll make one for you when you know what your arrival date is.
Next week is Jewelry convention, you wont get a table without a reservation.
Here is the Homepage:
http://www.walliserkanne-basel.ch
Here is a place where you can find other restaurants to your liking:
http://www.basel-restaurants.ch/
Enjoy yourself