Phone P&D Enterprise out of Edmonton and/or Wolverine from Winnipeg. They should both have them, or can get them for you.
I was looking for one as well, but I never got around to it. I was thinking that I might just go with the Daniel Defense Big Hole Upper Receiver Group from One Shot Tactical:
Link
This is the description:
The Daniel Defense Big Hole Flat Top Upper is designed and built with a .315 front pin hole to fit the early Colt lowers with .315 front holes. This eliminates the need to use an offset pin, which requires 2 screwdrivers during assembly / dis assembly of these rifles.
This upper comes with our .315 Push Pin, which makes the assembly / disassembly of the upper and lower quick and easy. It has a detent ball to hold pin securely in place.
This upper comes complete with forward assist, ejection port cover Indexing Marks and M4 Feed Ramps.
Materials & Construction
Precision CNC machined from a block of 6061 T6 aluminum and finished in hard coat type 3 mil-spec anodized black for a rock hard lasting finish.
Aircraft Grade 6061-T6 Aluminum
Military Specification Hard Coat Anodizing
Weighs only 8.5 ozs!
Made in the USA!