Guest with no name-
Try this. I've always sung it in E, but it's all I7, IV7, and V7:
I7 IV7 I7
When I was a cowboy, out on the western plains.(repeat)
IV7 V7 I7 IV7 V7 I7
I made a half a million pullin' on the bridle reins.
IV7 V7 I7
Come a cow cow yicky come a cow cow yicky yicky yea. repeat