Flat black or gloss black?
If it's flat, all my exterior stuff gets "SEM Trim Black". Bodyshop supply places carry it, usually about $17 a can. I sometimes find it a O'Reiley's too, although last time I had to ask for it and they got it out of the back, it wasn't on the shelf.
Good stuff, tough, doesn't peel or fade, everything I've ever painted with it stays looking great for a dozen years and counting.
Pete