Howard Whitehouse's account of the battle in "Science vs. Pluck" says most of the camels were left in the zariba. However, there were definitely plenty of camels inside the square, enough of them that they made something of a nuisance of themselves, forcing one face of the square to bow outwards. It's also said that the large mass of camels in the square impeded the movement of those Dervishes who managed to break through into the interior.
Anyway, you don't need mounted Camel Corps figures for this battle, the force formed up in square formation ready to fight the moment they left the zariba. In fact, nice as such figures are, you don't really need them for any battle. They were strictly for strategic movement.