I would try the local colleges or universities. You just never know, there could be a person just waiting for something like this to come up.
If you do find somebody suitable, I run a nanny agency called, Nanny and child. We offer a screening service which may put your mind at rest in terms of their background.
do take a look, and if I can help in anyway please don't hesitate to contact me.
Goodluck with your search!