I heard back earlier today from Mysti Ramesses who is still keen to take up the character in her alternate persona, Mysti-Maat. Consequently, Ma'at is no longer available I'm afraid.

There are still some plum goddess roles that haven't as yet been snaffled - Nepthys, Nut, Heket, Tefnut...probably more but that's all I can recall.

Perhaps one of these takes your fancy? There are also some plum male gods going for a song but I hesitate to suggest those ;)