Try here:
http://www.batteryspace.com/
They have all types of batteries, in any size and configuration you want, with any connector. Their prices are very good and theer is a lot of good battery tech info on their site.
I use them for R/C batts and for divng equipment, etc. and the packs are great.
For tanks, I have been gettting 5000mAH "C" batts x 6 packs in a "brick" configuration. The best batts for tanksin my opinion are Nickel Metal Hydride (NiMH) batts. I'm still not at the point of switching over to lithium batts cuz I don't know enough about them, but Batterspace has them too if you want lithium instead of NiMH.
Here's an example of a pack similar to what i use. You can request the desired connector:
http://www.batteryspace.com/nimhbatt...ledevices.aspx