Texas State Dept of Agriculture in Austin. Also check with your Texas A&M Cooperative Extension Service office which is usually in your local county courthouse or county or state offices blue pages of the phone book. You probably have other agriculture schools in Texas as well. I'm not aware that ALL imports have to be inspected but I do know many which are shipped into the citrus areas along the Gulf and Rio Grande areas must be inspected. They are trying to prevent disease which might ruin ag industries such as citrus.

Try this link. It is a good start. This topic can be quite complicated. The Federal Government as well as all 50 states have their own regulations and specific quarantines regarding plant material.

Here is a link that might be useful: USDA