Bean Farm or Reptile Basics are good places to order Flexwatt from..
If you're using Flexwatt you don't necessarily need six separate cords, I've seen people wire a certain amount of feet of Flexwatt to one cord, not sure exactly how they've done it but I'm sure there are quite a few threads on here, just use the search option.
Other than Flexwatt... I'm sure you could use Ultratherm heat pads, but that would mean plugging in six individual heat pads, would be more expensive, and would probably need more than one thermostat! Go with Flexwatt..
EDIT: Here is how you can wire multiple strips of Flexwatt to one thermostat on a rack..
http://www.reptilebasics.com/images/...t_parallel.pdf
Here is another great explanation from Slitherin' Sisters:
http://www.slitherinsisters.com/how-...e-flexwatt.php