I am overflowing with work and now have a waiting list. Good news but a headache

In September I will be well over if I don't act now.

How and where has anyone else advertised?

I have found all my previous assistants through Gumtree and they have been excellent.
My main assistants have always been live-in au pairs who I find through aupairworld. They have been excellent too and normally stay for up to a year.