They have them on the new web site, both GEL and AGM replacement for T-105 type.
No 8volts yet. But as they have lower AH, I would use 8 of them on a 48v system for longer range.
Check out specs: (I like a lot more the AGM's)
GEL:
http://www.trojanbattery.com/Products/6V-Gel6V.aspx
AGM:
http://www.trojanbattery.com/Products/6V-AGM6V.aspx
But as said by Mike, we have the Discover batts already with much more options to choose and of course there is 8v and 12v on them.