You are a descendant of Francis? Fantastic!!!
You are probably aware that Bill Forrest (The Descendants of Samuel Swain) stated that Francis died of typhoid on 22/2/1877 at Rangers Valley, near Tamworth, NSW, and there was no record that he had married. I, too, have searched for a marriage record without success.
BUT Francis's mother, Patience, in her will makes provision for "Frances Sarah Swain daughter of my son the late Francis Swain." I have searched without success for a New South Wales birth record for Frances Sarah.
So no, I haven't found any more details on the family in Gloucestershire, but if my enquiry has brought to light some information on Francis's line I'll be delighted.