Swampers
I posted a link to a DOT approved Swamper, I realize they are not the roundest tire or the quietest, but they are a DOT mud tire, not an atv tire.
Is a super swamper too aggressive for what you need?
What 4 bolt pattern do you need? Discount tire lists 12 different sizes of 4 bolt patterns. For my trailer, 4x4" really limited my wheel choices.