I am something of a vintage speaker devotee. I peruse that market. I think what you may be seeing is a rebadge of a more typical brand because Mercury is unknown to me, not that I know all of the brands.
What happens when you google it or try the vintage speaker pages. There aren't many broad vintage speaker pages but with a specific brand you might get a hit.
As far as collectablity goes this is not one I notice people are seeking.
It's broad range and high sensitivity are typical of a late 1950s to early 60s speaker. I'll do some searching myself. For some reason I think you may have a "University" made driver. Have you seen the front is it coaxial?
What happens when you google it or try the vintage speaker pages. There aren't many broad vintage speaker pages but with a specific brand you might get a hit.
As far as collectablity goes this is not one I notice people are seeking.
It's broad range and high sensitivity are typical of a late 1950s to early 60s speaker. I'll do some searching myself. For some reason I think you may have a "University" made driver. Have you seen the front is it coaxial?