Do you have to reserve these in the US? if not how do you finc out where there stops are to get tickets??
No, you don't have to book in advance. Go to www.paris-opentour.com.
The URL for another tour is www.carsrouges.com.
Definatley do NOT order this ahead,, first of all, these buses are fun, I did them when I took my 14 yr old son for his first visit,, but, they are entirely weather dependent. Yes, you could sit inside,, but the real fun is to sit UP TOP.
My friend who has never been to Paris before and I went for two weeks just a few weeks ago, August, and it rained most every day lightly, and it was cool, and it would not have been fun to have bought the bus passes for those days. As it was we never got around to using the L'Open tour bus at all.
Second of there is no money savings by ordering ahead, and in fact it may even cost more.
Go on the web site, see the routes, any where the bus stops is where you can buy your pass as you board. Of course it stops at all main tourist sites, so even if you can make your way to say Notre Dame or Eiffel tower you will find the bus stop. The signs are yellow and green like the bus.