Variant with shields and moustaches (likely this one will be in final version):
Here is the low-level slinger unit, for which I have skinned mercenary and rebel version as well.
(Sorry about the rubbish screenshotting, I was going so hard for the angle I forgot about that stupid blue text you get using movie_cam... anyone know a way to get rid of it???)
Addenda:
-The shield. I made a plain wooden design and then simply varied its hue depending on the faction (slave, merc or britons). There is evidence for round shields in Iron Age Britain, although it was not the norm. I think it is unlikely slingers generally carried shields at all, so I chose the most lightweight type I could think of. For the variant used by the Slinger Warband unit, I decided to keep it simple. The chequered design is found on one of the bronze miniature shields from the Salisbury hoard, and the blue spots... well, they're just spots, it looked a bit plain without them. 
- Models. Really, all I have done with these units is reskin them, because I haven't a clue about modelling. This means that both units have a knife as their secondary weapon. However, I think it would be very cool, if possible, to give the Slinger Warband unit a spear instead; EB2 is doing this for one of their sling units and it looks brilliant. There's no rush with this though, the units are obviously fine without.
- Unfinished. These guys are not yet polished off. I still have to write the description for the top-tier unit, generate the sprites (doing it now), and make the UI pictures. When all that's done, if anyone needs them to incorporate them into the main build I can send them directly.
Bye for now!