Mercury? Never heard of that brand. Not mentioned at the "SANE
" site at all. To be honest, scanners are a problem. The only one I can think of that works out of the box and is currently on sale as new is the Canon LiDE20. If you search around you may get the higher res but superceded Canon LiDE30. But don't take that as an endorsement of Canon, because their support for scanners is poor and none of their other models (including the similarly numbered LiDE35) will work under Linux at present.
If SANE cannot find it, you other chance is that the manufacturer provides a driver for it. This applies to some Epson and Brother scanners. Try searching the manufacturer's web site.
Don't hold out much hope, though!