Re the L78M05CDT you could also try a Traco Power TSR 2-2450.
This is a switchmode drop in replacement for LM7805 with a 2mA idle current, rated for 2A. It does not need heatsinking. I've used them when repairing the power supply in multimeters which have closed cases and no active cooling (Fluke 8000 series bench meters).
Warren
