There's someone in Tacoma (don't know where you are) who sells pullets from their farm. They have a CL listing for a bunch of different breeds of different ages. Search the following phone number and you might be able to find some pullets of the same age as your girls and integrate them really easily. (253) 327-5039 is the listing phone number and all sorts of breeds pop up.
If Seattle Farm Supply doesn't end up having the ages I want on Saturday when I return the rooster I got from them, I'll be going to Tacoma for a few girls