Cedar Rapids, IA
What make of transmitter? Battery packs for popular transmitters are easy to come by. A good hobby shop in your area might have them, or you can buy packs of the appropriate shape and capacity from places like Tower Hobbies. You would need to solder the proper connector on that kind of pack, but then you have one on the old pack that can be reused.
If you are skilled at soldering and have the tools and access to eight AA nicads of 600 mah or larger capacity with solder tabs on them, you can also make up a pack very easily.
Your heli flight pack should have a power switch, and that power switch harness should have three separate pigtails on it. One goes to the battery pack connector, one goes to the receiver's battery slot, leaving the third pigtail flapping in the breeze. This extra pigtail is the plug used to charge the receiver battery, and should mate with the charging cord coming from your system charger.
The charging lead quite often just dangles out the bottom of the canopy for easy access, or you can mount it to either the frame or the canopy in an accessible spot.
This picture shows the charging plug mounted on the under side of the canopy (right side of picture, the black rectangular socket with the rubber flap on it):
While in this picture, the charging lead is that pigtail and connector on the left hand side of the picture by the skid strut, and it's just dangling.