I already suggested this when I signed up. But I'll repeat it. This is something I haven't seen implemented yet when I searched in Google for pro-Israel T-shirts.
You have a t-shirt with a map of Greater Israel (not as it is today, but as God said it should be). Something like this (I don't know if this is a correct map, because I found it on an anti-Zionist site):
Underneath you have the words from the Torah where is says "From Nile to Euphrates." You have it in English or in Hebrew or both. I know I would buy several for my entire family.
In the same vein, I have seen gold pendants in the shape of countries. Like Italy's "boot," for example. Usually, they are not that expensive, because there is not that much gold that goes to make them - they are quite thin. Why not make a similar pendant in the shape of Greater Israel with some Hebrew writing on it? I am sure, a lot of young people would want one.
And even to expand that idea. A lot of countries have dreams about their former glory. Why not make t-shirts and pendants that say Greater Albania or Greater Armenia or Greater Poland, etc.. This could be a really good source of extra income for JTF if one sells these through ebay, and there is not a lot of overhead.