No "national" calendar that I know of.
Also, it's a misconception to think that "unsanctioned" events are any less serious than KCBS or MIM! Often the only difference is the amount of prize money! :D Bragging rights are seriously sought awards at local and regional events.
Check with your Chamber of Commerce and those of surround towns/cities. Local papers will sometimes have info.
Another option is to sign up for a sanctioned event and enter the backyard or amateur division. One good thing about a sanctioned event is that you'll usually have certified judges - at least that's the way it's handled by the FBA.
Southern Brethren BBQ Competition Team
"It's all about getting paid!" - Myron Mixon
"I love being hated in my hometown!" - David Hair
KingFisher Gator Rotisserie cooker, WSM, Stainless 5 burner with IR gas grill, Turkey Fryer, Weber JD Commemorative grill, slightly used Bandera chamber for future use as a cold smoker, Masterbuilt 40" insulated ELECTRIC smoker