Philippe,
I
do know that to import a plant to the US, I must have an import permit from the USDA Animal and Plant Health Inspection Service (APHIS), and that the foreign shipper must provide the CITES docs from their government and a phytosanitary certificate, certifying that the plant is apparently free from insects and disease.
I don't know Thailand's import requirements, but I'd bet they are similar from the CITES and phytosanitary requirements.
This might be of some help:
USDA - APHIS - Plant Export Information
I got this info - inspection offices - from the Washington Department of Agricuture website:
801 SW 150th St., Ste. 217
Seattle, WA 98166
Fax: (206) 439-3724
Cyndi Baumgardner, Plant Services Specialist
Phone: (206) 439-3722
Tobin Gilbert, Plant Services Specialist
Phone: (206) 439-3725
I'm sure that if your brother spoke to them, they would help him through the process.