I buy seeds from companies outside the US all the time and have been doing it for years, no problemo. The vast majority of seed businesses abroad do not even ask you to fill out the "small packet" form from the USDA.

Here are a few sources for interesting seeds
j l hudson seed has CARAGANA, PURPLE GOOSEFOOT Tree Spinach, and many more

Johnny's Selected Seeds has a few interesting things

http://www.bountifulgardens.org/ Bountiful Garden has a perennial vegetable combo pack of interest as well as a perennial grain.

I haven't found Tagasaste/Tree Lucerne (Chamaecytisus palmensis) but suspect it may be a serious invasive species here as it has become in Australia. I would not advise planting in anywhere near open space.

Pigeon Pea - I was found these at a US seed company but when I put the name of the company in this post the Garden Web Folks blocked it for some reason???

Here is a link that might be useful: J L Hudson Seeds

I, too, would love to find Tree Lucerne (Tagasaste) here in the US. I have heard of people trying to order them from overseas, but never with success. Does anyone have any ideas, or if you're growing it maybe I could buy some seeds and/or get tips and experiences?

Thanks!