"Stainless steel" is a misnomer, it is correctly called "corrosion resistant steel". Some titanium fasteners are offered but they are very costly, not as strong as steel and are subject to embrittlement and fatigue cracking. They are used in aircraft where weight is a prime concern but special design and fastening techniques are needed as well as frequent inspection/replacement. Some so-called "weight weenies" buy them as a weight reduction method but I would not touch them myself.