floating tenons and augers

Is there a preferred and efficient way to cut the long slots in beams to receive floating splines. I need to make 12 of these slots 2"x4"x16". Also, does anyone know of a source for 1 7/8" and 2" power ship augers capable of drilling to 8" depth?

Last June I got a 1 1/2" bit that's 16" overall from a industrial supply house. They said they stock them for plumbers and gas companies to use to bore threw sills for pipes and gas lines. I'd call around your local plumbing supply houses and see what they have or could recomend. Good Luck. Jim