Haggis in Denver?
You might try calling Edwards Meats in Wheat Ridge, http://www.edwards-meats.com/. They seem pretty comprehensive in their meat-related services.
But my guess is you're out of luck on pluck (lungs and heart) - I don't think it's legal to sell those for consumption in the US. I'm going to try to make an Americanized haggis - in a crockpot, no less - this year; we'll see how it goes. http://crockpot365.blogspot.com/2008/...
12280 W 44th Ave, Wheat Ridge, CO 80033