No, they don't come as standard, but some builders would supply them on demand.
There used to be a company called, amazingly, 'The Yacht Leg Company', don't know if they're still around. Try a Google or PBO classifieds.
They are often just wood, and bolt to a threaded hole fitted throught the topsides of the hull, which is, in turn, fitted to a strong backing pad. The leg extends up above the freeboard to enable taut lines to be rigged fore and aft to keep it vertical.
The luxury versions have a spring loaded foot, although I'm not sure it's really worthwhile.
What boat do you have? Asking because some will go bow down when they dry....