Try Colfax Tractor Salvage, ColfaxIA 800-284-3001 they have several M_M2_M3 series. I will be going there later today with a friend from this board and find out what is in stock right now.
Stopped in at Colfax today and all of the newer M2's and3's were already missing the long shoe. Check with Worthington Tractor Salvage, they have several locations nationwide and are on the Internet.
Where are you located,I'm from central North Dakota and know of a fellow that wrecked one out and made a sprayer out of the combine. He has most all of the combine threshing componets for sale. He is located in linton, ND. If your interested I can get you a phone number.