Sing Song Kitty by Doc Watson

Rude and Rambling Man by Doc Watson and friends on Pete Seeger's public access show Rainbow Quest. The harmonica doesn't really stand out much, but it's there adding a layer of depth to the fiddle which is neat and not something I hear often

Edit: also Bob Dylan has a lot of harmonica heavy songs, but I'm not a fan so I couldn't tell you which ones are worth listening to

Second edit: also Woody Guthrie has a bunch of songs with harmonica as well, if you're not sick of old folk music