Well they are hard to find and you'll be lucky to get one but.....
I absconded an old cargo parachute. They only use them about 10-20 times or so then discard them. I fly with Civil Air Search and Rescue, so that was my contact. You might want to ask one of your military friends for one?
They are quite heavy, however what I did was cover my boat with it and then take a pair of VERY sharp sheers and cut the bottom edge off around the perimeter of the boat. This made it a bit lighter as I turned a round object into a rectangular object, thus removing alot of dead weight.
I have a 41 foot offshore boat and it covered it quite nicely! I am in a heated indoor storage facility that is kept above freezing all year long so I have no worries about engine blocks freezing or anything like that, but it's nice to keep the dust off as in the spring it cuts down on cleanup alot.
In the spring I wrap it up and take it to the industrial laundry and run it through a wash cycle and fold it neatly for next year. (My buddy works at the hospital in town with a huge laundry machine!)