The item you've described is definitely sold, and usually described
just as you did, a female-female connector with RJ-45 connectors.
Here are two sources to buy them only for a few bucks:
Lindy Computer Connection Technology
[ http://www.lindy.com/us/productfolder/06/60184/index.php ]
[ http://www.trianglecables.com/cat5rjshielc.html ]
I'm almost positive I've seen these at radio shack, however. They
usually have a slightly better selection than regular computer stores,
for these types of things. Hope this works!
I should also point out that if you extend Cat5 cabling too far, the
signal will significantly degrade. 5-10 feet should not be a problem,
but make sure you're not using something like a 50' cable just coiled
up to extend that 10 feet, because you will likely run into problems.
If you require any clarification, please request it, especially before
rating this answer. Thanks for coming to Google Answers!