In the U.K. they may be bought from https://www.thediceshoponline.com/di...ompass-D8-Dice

in the U.S.A. from https://www.gmdice.com/products/d8-compass-dice

but there are many other suppliers. Just perform an internet search on 'd8 compass dice'. You may find better prices.

If you have a normal d8 just assign a different direction to each number.