[DKanger]

John Rickets (1815-?) worked in Mansfield, Ohio from 1850-circa 1890.
Henry Elwell was a lockmaker from Seneca county, Ohio.
There's a book called "Gunsmiths of Ohio", which is fairly pricey, that may contain more information, and a large collector's association located in Ohio dedicated to Ohio made guns. You might be able to google them up and contact them.

Lower grade fowlers have relatively little value, unless in pristine condition. Most sell for less than $500. "A picture" is of no value. Collectors and buyers will want close up, detailed pictures showing the features of the gun.