Hi jayflash,
The majority of the WriteRights should be for colour screens. If you go to Office Max again, you can look for any of the following:
WriteRights for colour Palm PDAs
IIIc, Tungsten T, m505/515, and so on.
There should be quite a few WriteRights for Tungsten Ts (pretty common).
Palm V, IIIe, m105, Zire 21, and so on are monochrome screens. (Note that some Zire and m series are in colour now.)
All Sony NX/NZ series are for colour screens. Most T series are too.
All WriteRights for Pocket PCs are for colour screens.
If the staff can't help you, as long as they have display models of the different PDAs, you can turn one on and see if the screen is in colour. If so, find which PDA it is, and try to find the matching WriteRights for it.
I think that you are looking for Black and White ones? (That seems to be what people recommend.) If that is the case, WriteRights for Palm V PDAs should be a good bet--most office places still stock these.
Hope that helps. If you need more information, please let me know.
Cheers,
eric t