Hi Thomas:
For clarification purposes, are you asking "How does one go about introducing globe willow 'Navajo' trees into Illinois," or are you asking, "How were globe willow 'Navajo' trees introduced into Illinois?"
I hope you're not asking the former question about how to introduce globe willow trees into Illinois as I will tell you quite plainly, "Do not."
If you're asking the latter question, I will have to defer to the nursery and ornamental horticulture folks in the state.