Really easy to make your own, use the link below which you can change the number in series and parallel etc and it will show you how to connect, also will show you how to connect the balance wiring if using it. Use the 2nd down diagram/converter on the page. You only need protected cells if running in series so for your planned pack their is no need:
http://scriptasylum.com/rc_speed/lipo.html
The good thing about making your own is you can choose the quality/power of the battery used. 2 links below to ebay sales of very good batteries:
Xtar protected 18650 cells 3100mah
18650 panasonic cells 3100mah
battery pack shrink tube link
Plastidip to waterproof your pack
Was also going to mention that smudge makes very good battery packs (www.mtbbatteries.co.uk) :wink: