My suggestion is to connect with local herpers. Sheds happen fairly often and don't hold much value to someone who has a bunch of snakes, I don't think you'll have any problem finding someone who is willing to sell you a shed. Heck I'd give you 10 of em for free if you wanted, but my largest snake is only 7lbs and wouldn't fit your criteria.
Very creative and cool idea. Modge podge will work just fine for your next project and look very nice!