I've found different kinds everywhere!
Our dollar store had a good selection a couple months ago but had sold out by the time I returned to get some.
Target in the outdoor/patio section had shoulder strap medium size ones, but the bottles were round and looked uncomfortable to carry. I think they had some other kinds too.
Toys R Us in the front summer/swimming section has (or had -- I got the last 2 on clearance in our store) large flat ones w/shoulder straps that you can also drink from. Maybe too heavy?
Wal-mart had a varied selection on the row with the fans (which was at the border of hardware/automotives, including expensive misters and hand-held pump spray fans. I ended up buying necklance fans with no misters for my dds there; they're the kind with a "cage" over the fan and they'll blow up your chest-neck-face while you're wearing them, hands-free. Less than $3.00. These were hanging from displays near the ends of the aisle and I almost didn't see them. I figure the dds can use the fans and we'll mist them every now and then with our big bottles.
hope this helps someone!
kayt