Did you search old Mamapedia questions? I know someone asked something similar last year and got a lot of responses!
And I always recommend AAA's free (to members) travel agency. They have a lot of up-to-date info, discount info, coupons and so on.
Re the liability issue mentioned below - have you seen the Road ID bracelets? They are designed for runners who carry nothing with them - no phone, no ID, etc. My husband and son have them and they are great. You can customize the band with contact info, either for the scouts' homes (not too practical in this case) or the troop leader's info. It may be expensive but I'm sure there are cheaper alternatives out there. Maybe they can make something as part of a merit badge or just a project? And DO order matching TV shirts if they won't be in their uniforms. It does make it easier to round everyone up, and sometimes other tourists are more likely to let a group stay together instead of cutting them off in passing.
Have fun!