I think you could definitely find people willing to do 'flex care' .... if you are able to book your needs in advance and be flex in return cause often providers who do this are trying to manage it with several families and somene else might beat you to a day you want
You could post an ad in the classifieds 'looking for' with more details and providers looking for spaces to fill often search there everyday but do not necessarily have time to look on the forums