i believe that the main problem about adding anything else to a firebelly tank, is the fact that they secrete some sort of toxins into the enclosure.

i personally just went from a fully aquatic (with a small land portion) to a fully land with a couple of water bowls enclosure... my firebellies are loving it...

in terms of the small turtles, you kind of need to know where to look. they are readily available where i am in texas. a good place for you to try and check, is if you have any local swapmeets where they also sell animals... some times the vendors will carry them. thats where we got ours! $5 for the turtle itself... lol

it sure is a shame you dont live closer to mcallen texas, we have to find our little turtle (maybe 3 inches in total length) a new home. due to the fact that my apartments freaked out on us, and i will not give him a non aquatic home. so he has to find a new home.

i would try the swapmeet if you have them... for the little turtles