I bought some BMW spacers with longer chromed bolts for my widened Jalpa rear wheels and the bolts fit perfectly. However the socket needed for those bolts is 17mm rather than 19 mm for the original bolts. They also protrude a little more (hex is taller), which is not a problem for the rear wheels, but may not look as good on the front.

Here is an eBay reference to a spacer set similar to what I purchased:
http://tinyurl.com/258bg6
I would guess that a BMW dealership will have those bolts as well.

Laust