Are these Alps decals? I have had success with using a color laser printer. The blue toner is darker than the Alps blue and wouldn't have the banding issues you have.
Alps "banding" is a totally different artifact. This effect is halftoning.
But your solution is valid. Laser printers have finer halftone screen frequency. But ink jet printers are even better since they use stochastic halftones with randomly scattered dots.
Like you said, since these decals are applied over white surface, they can be printed using a printer which does not lay down a layer of white undercoat. So any Laser or ink jet would work just fine.