I heard there are a couple of places just outside Basel City, otherwise this mail order store in Germany has a some good products, a little bit on the expensive side maybe.
www.ullapopken.ch They have nice clothes for XXL.
Hirmer in Munich is Germany's biggest men apparel store, including standard sizes.
However, they do have a branch in Stuttgart specializing in oversized clothing and will open another store in Karlsruhe in spring. All their locations can be found here: http://www.hirmer-grosse-groessen.de/Bremen-HGG-1/
If you need to get it mailed to you, you can use this service over the border which will accept deliveries for third parties for a small charge. Contact [[email protected]](mailto:[email protected])
They charge Fr. 5.- for a package.
for next year you can call http://www.knie.ch/