This is the form you want as a printable file:
http://www.aphis.usda.gov/ppq/forms/ppqform587.pdf
They shouldn't charge you anything for this as you are not a commercial importer. This is the preceding page that will let you file this form on-line. But I personally wouldn't want to have to keep track of another pass word.
http://www.aphis.usda.gov/permits/ppq_epermits.shtml
When I filled this out 20+ years ago (the form hasn't changed in all those years), I put orchids under scientific name and plants under plant parts. For country, I listed every likely country I could think of, infact, I even think I put an 'etc.' in there. One of these days I'll pull out my old permit from the basement, its very well burried right now, and see what I wrote. Course, they may not be so aggreable about the 'etc.' these days.
To fill out the section for port of entry, I suggest you call the numbem on the form to ask about it. If you are ordering these plants, they will probably come by plane, so you can limit yourself to airports. I once ordered by airmail, expected the plants to come in thru LAX or Miami. The plants were held up a week because they came into Portland, OR, which was not on my list, and only got forwarded when I missed them and started calling around to find out where they were.
Here is one you need to read:
http://edis.ifas.ufl.edu/EP043
Here is something you might find useful, but you can skip over most of it:
http://www.fas.usda.gov/itp/ofsts/us.html
Cynthia