I have heard there is diving off the Banana Islands of Sierra Leone, but can’t find a reputable dive shop to rent equipment from.

Try Franco’s Diving Center in Sussex, Sierra Leone. They are located off the peninsula road to the west of Freetown–the road is really horrible, but it’s worth the trip. Call Franco: 232-76-642-003 or his wife Florence: 232-76-744-406
I never actually went diving there, but I’ve eaten at the restuarant and stayed at the guest house. It’s one of the best places we found the Freetown peninsula area while living there for nearly a year and a half.