Body parts are already hard to find. But engine/chassis parts are not a problem, for the most part, you search for "2003 Mercedes SLK320" and, most of the time, the part can be ordered if not already in stock locally.

Just verify the air compressor is working, get a tire plug kit, a spare crank sensor and change the belt and battery every four years. (Not to mention transmission service, coolant flush, etc from time to time.)