Depends what you want it for, but Chestnut ebonising lacquer might be suitable. Comes in an aerosol spray can and, as the name suggests, gives an ebony like finish. Generally available. Axminster have it (order code 118024, £5.36 for a 400ml can).
Black is certainly available in the spirit stains, depends what you want to do with the finish.
If you want to let the timber, grain or whatever show through go for the spirit stain. If not go for the ebonising lacquer, I use this on the inside of hollow forms to give the "black hole" look.