It may not be recommended, but I've had good luck with adding a foot or so to the antenna. Can the receiver be relocated to be closer to the transmitter?

Any transformer that puts out 3 volts DC at roughly 225 mAh should work fine. This one should easily be close enough:

http://www.radioshack.com/product/index.jsp?productId=3875402

Just cut the end off, meter, and solder in place of battery.