David,
You can't purchase the tape off the shelf, as far as I am aware... it is industrial bifilament packing tape. The sheets are also hard to find, especially in the bay, this time of year. People have purchased them at Home Depots and Lowes, but you may have to go to a lot of them to find it, if it exists at all, or go out into the east or south, away from the city.
Also, what are you going to do with it when you fly back?
You've definitely set yourself a challenge here... ;)
If you really want to do this... I would order tape online IMMEDIATELY and have it shipped to someone in SF area for you that can hold it. This place might do:
http://hexayurttape.com/
Secondly, I would start calling hardware stores in the bay area and asking them if they have R-Max or Tuff-R 1" Polyisocyanate board. It HAS to be polyisocyanate. If they don't know what that is, tell them it is "very stiff. Much stiffer than normal insulation board. It doesn't bend at all". The moment they say "yes, we do", make sure they have enough panels in stock, and offer to pay them right then and there for them, and hold them for you when you come out.
Lastly, if you are not going to take the HY with you when you leave, find someone at the burn who wants it, and can take it back with them. Or store it in Reno in a small storage locker for next year.
Also remember you'll need to secure it down to the playa with rope and rebar. So get a big roll of rope (they have a lot of that at hardware stores cheap), and 4-6 pieces of 3 foot long, 3/8" rebar. you take two pieces of water pipe, put one over the rebar, and let 6" peek out the top. then put your foot down on it, put the other pipe over that 6" and bend it into a hook.
Hope this helps!