I got mine at a flea market. They are so handy that I ended up getting another one and then one for my daughter when she went off to college. Helps when you have to bring in groceries from the garage to the house and when you are moving into a new place and if you have to go to a laundrymat and when you have to return a whole lot of books to the library -- I use them for all sorts of things!
Warning, do not push them, especially the cheaper ones. I work with the elderly and two clients were pushing their empty carts, the carts hit a crack in the sidewalk, collasped and the ladies fell and broke bones.
Yes, if you sometimes see folks pushing their grocery carts in the side streets instead of up on the sidewalk, don't automatically curse them. They may be trying to bypass a particularly crummy stretch of busted-up sidewalk. I twice hit a broken spot in the sidewalk after dark (the same place both times - shame on me!) and, of course, the front wheels pitched down into the shallow hole and I followed sprawling to the ground.
Re: pushing vs. pulling - pushing is always easier for the long haul. Just make sure you can see where you're going. If you have to go through a large crack, tilt the cart back on its rear wheels to go down, then forward on its front wheels (if it has them) up on the flat to push out of it, or turn the whole cart around and pull it through the hole.
I've purchased 3 grocery carts since I got rid of my car 10 years ago. Two of them probably gave up the ghost due to being grossly overloaded far too many times. All came from the Container Store. I'm presently using this one http://www.containerstore.com/shop?productId=10007349&N=&Ns=p_sort_default%7C0&Ntt=grocery+cart The handle is a little short; if you take long strides your ankles bump into the cart. Otherwise, although it's pricey, it's light weight and has held up since I stopped trying to move furniture with it. :) I bought the liner for it later. I've found that really useful since you don't have to worry about getting caught out in the rain and the grocery bags or other items don't fall through the openings on the side as sometimes happens. Of course, with the liner installed, the cart doesn't fold exactly flat, which may be a problem if you're short of storage space.
i have bought at many places but mostly small asian stores liek on granville and broadway many colors i too have broke a few...current one red and is holding up in past had black royal blue originalones were silver.