Whilst looking for a cheap source of ebony to make banjo wedges, I came across the following website.
.http://www.earlswoodinteriors.co.uk/african-blackwood-bells-3996-p.asp
They sell exotic woods for craft projects and I ordered what they list as black wood bells, it cost me just under £10 with the postage and they sent me a chunk of wood about 4"x4"x5". It was just right for the job and I've already made an fitted a couple of wedges to one of my banjos. I don't know if they ship outside the UK but this info may be of use to our British Members.