Is there a piece of equipment that connects to a wireless network and provides ethernet ports to clients?
You can use a wireless ethernet bridge. One example is http://www.linksysbycisco.com/US/en/products/WET610N
You can do it with commodity wireless router, set in a bridged mode. If the build-in firmware does not support this, you can try some of the opensource firmwares like dd-wrt, openwrt, tomato, etc. Check the hardware support list for these.