There are stainless "deck screws" They come from Screw Products Inc, made from 305 Stainless. I buy the #10 X 3" & 3 1/2" in 5# containers. I also like that they come with the T25 Star Drive so that your driver doesn't slip in the head. Have been using them for 5 - 6 years.
I especially like them because they don't corrode making it easy to take them out an reuse them. The reason I reuse them is because they're not cheap.
I see from their web site they come in other sizes and they do mail order.
SS screws ClickyI also bought smaller sizes from my local hardware store.
I first started using them because I build a lot using the green pressure treated lumber - the chemicals in it will ruin standard deck screws so they weaken and fall apart. After a standard deck screw has been in green pressure treated lumber for a year or two, you can't remove them. Either you have to use SS screws or galvanized lag bolts.
Bill