SuperOne Kenwood used to have one, not sure if they still do. Used to be many of the grocery stores had them, but some are long gone.  Sometimes they still post in windows. You could also contact leasing companies to see if you can post them in the windows of vacant or in other key areas. I'd scour the downtown blocks and businesses, and West Duluth areas and the Mall too - and along bus-stop areas / in bus-stop shelters or in-bus posters? Maybe contact the DTA? Jefferson stops / the airport?  Taxi companies?

I've noticed posters for local events on the doors at Mount Royal Bottle Shoppe and at the Duluth Library - Downtown and Mount Royal. 

Also, St Scholastica (and all the colleges; LSC, DBU, UMD, UWS) and the Whole Foods Co-op. Maybe the food shelves and Ruby's Pantry? Churches? Blood donation centers? Coffee shops. Toasty's, Jefferson People's House, the Bike Cave, Great Harvest Bread Company.

I'd also check into other community places -- maybe even at the farmers markets in both Duluth and Superior, and Damiano Center, Chum, Second Harvest Northern Lakes Food Bank and even the women/teen shelters? The Park and Rec Center on Lake and Fourth Street. Downtown apartment/housing bulletin boards. Washington Studios. Loan and pawn shops. 4th Street Market.

Plus! Make a Facebook page and Twitter account and Google + , and more. Use your social media!!!