I wouldn't worry to much bout not getting your seeds through customs. They rarely get held back. Customs tends to deal more with actual live plants since there at a way higher risk to carry diseases and/or pests which may attack our native plant species. I've delt with this while buying my succulents. I've gotten seeds and plant's out of the US and had no problems with customs. All though buying plants from over seas is a risk due to the delay in transport. Seed's on the other hand do just nicely.