You will have to get it checked to be sure. At stock height you *should* be within spec but that is not always the case (as grip pointed out) you could have worn springs or hit something etc. that put you out of spec.

For the front there are bolts you can get from mercedes. Some call them "crash" bolts, others camber bolts. Should be able to find the part number easily with a search. These offer a static amount of adjustment as you can only install them 2 ways ( one way for positive adjustment, one for negative) Cant remember exact cost but I want to say like $15 a piece from the dealer. You can use a total of 4 (castor and camber on each side) depending on your needs.

As for the rear there are a couple parts lists you can use to build your own sets. I think speedybenz makes some for the SLK that can be used or you may be able to find some used ones on the forum that mikeR or other members have made.