Cassette washer

I was changing a tube out today on the rear wheel of the ST1 (3/4" nail). After the repair miles away I realized that the large washer/spacer that goes between the cassette and the frame was missing, making it impossible to use the highest gear because the chain doesn't fit, not to mention the alignment of the derailleur is off (possibly other problems in not aware of). I went back to the place where I changed the tube, but I can't find the spacer.

Does anyone know if can I order it? If it's too expensive to get it to me in the US, can I use a stack of washers instead?

Thoughts?

Thanks.
 
I got in contact with Stromer and they are sending me a spacer. In the meantime, after a trip to Lowe's, a stack of washers seemed to work ok... provided that they didn't rotate with the real wheel rotating. It took a little experimenting.
 
If I remember correctley, there is a thick washer on the inside of the chain-stay on both sides of the wheel that is the same size. It keeps the wheel and axle from falling out of the chain-stay once it's positioned correctly - so I believe thickness may be important.