Well I would have to say that you've stepped on kind of a landmine. Well actually not a landmine, but it could be if you're not ready to get your feet wet. Toon Generations are a delightful set of models. They exist both here in Iclone and in another program called DAZ Studio. Creating clothing for them is not for the faint of heart --by what I mean to say is that if you want to make custom stuff for them, you're going to have to get ready to step out of your comfort zone. You're basically going to need a program to model the program and a program to develop the rigging for the clothing so that it follows the bones of the figure when you animate it. Often times, these are the same program, but depending on your budget, level of skill and resources --more than one way of doing this can be available to you.
Much of the documentation on developing clothing for a figure is based in 3DS Max when it comes to Iclone. In fact, there's an Iclone figure template already available in Max for you to create figures. However, 3DS Max is an expensive program and you're more than likely not going to have access to it. But that's not the only way that you can achieve your goal. If you purchase the figure set from DAZ, then it becomes much easier for you to develop clothing for the models. That's because DAZ Studio is free, and their rigging tools allow you to quickly rig clothing to any of their figures with the
transfer utility. They even provide a
developer kit for those very figures. If you go this route, then you will need 3dxchange in order to import the figures into Iclone after you've developed the clothing, and you'll need a modeling tool like
Blender,
Silo, or
Hexagon to develop the initial geometry to rig in DAZ studio. Blender is free, Hexagon costs 19.95 and Silo costs $79 on Steam. I will not say which modeling program to use other than to give you some suggestions because people's personal preferences differ. I own those three programs but I'm most comfortable working in Silo.
This is basically going to depend on how comfortable you are with rigging and modeling and how much time you're willing to put into it.