All entries must be signed and dated by the call maker. The calls must be made within the past year.
Midwest Nationals is the second largest contest and takes place during the Wisconsin State NWTF convention in Wisconsin Dells. It is usually held around the 2nd weekend in January. Earl Duckett is the contact for the contest. I'm not sure what his email address is but you can get it from the WI state NWTF staff.
http://www.nwtf-wi.org/ He can add you to the mailing list of call makers when it's time to send out entry forms
Grand Nationals is by far the largest contest and takes place around the 2nd weekend at the NWTF national convention in Nashville. I believe the contact is Karen Cavender.
http://www.nwtf.org/contact_us/ Southeast Nationals is the third largest contest and takes place around the first weekend of March in Raleigh, NC. I believe "heatman" on this forum is the contact for that contest.
Many states have statewide competitions themselves. You'd have to inquire with them individually if and when they are held.