Is there any service where I can describe stock footage that I need using human readable search terms and sentences and send out a search request to multiple footage archives at once, so I will not have to contact each one individually, that will then use real humans or otherwise search intelligently and send me a list of suggested and relevant footage clips?
I don't know what you mean by human readable search terms, as opposed to keywords or tags?
But for a meta search directory service I would recommend (know of)
Otherwise, ya, you would be going through each service looking for footage.
And many more... I am sure others can chime in with their favorite sites.