I don't think that there are any toasters made with very deep slots...you just have to turn the slice on it's side.
I recently bought a decent toaster (long, deep slots does four slices) which includes a bun-warmer on top...ideal for freshening-up rolls, croissants etc. Only £15 at Lidl.
Some advertise deep thick slots but they're not that great really. As previous posters have said... stick your nice thick doorstep slices under the grill.