Have to agree completely with Angelnorth, of all the blacks for clear stamps, Versafine comes out best. We recently had a new product launched over here, via Chocolate Baroque, called 'Clearly Better'
inkpads, a blend of dye & pigment ink,designed to be used with clear stamps. I ordered a black one, and gave it a try out, and posted the results on my blog, here
I found it as good as, but no better, than Versafine. I tried it against most of the well-known black inpads, and have posted up the images from each. So for a good all-rounder, definitely go with the Versafine. I also know that in the USA, its possible to get a bottle of refill ink for the Onyx Black, although they DO indeed last for ages- mine must be four years old & still going strong. But worth getting one in view of where you live, and replacing supplies.