They shouldn't have a problem. Compost is a great way to get nutrients to your plants organically, and manure is not vital to a good compost mix. Manure is kind of already composted, which is why a lot of people use it alone on their gardens (tilled in of course, never just straight on the plants), and it can help enrich a compost thats lacking a little, but really isn't necessary. Also, if they wanted to get manure, they should contact local people who do have livestock or fowl (many people don't suggest using chicken manure because it can be a little harsh sometimes, but I know some people who have had great results with it) and ask them about picking some up, assuming they have a truck they can use and don't mind riding home with the smell. A lot of ranchers are happy to let someone else shovel out their barns for them.