Check with your local agricultural authority -- in the US, they're called Department of Agriculture.

They can tell you what's needed to import plant material. Depending upon what you want, could be a lengthy, complex project.

Perhaps a local nursery (a "collector's" nursery or one that specializes in foreign plants) would share the process they go through.

One thing that sometimes happens is people think they have to bring in something that is actually already on the market here. What are you trying to get?