I have used these Bern audio chips on my hard hat (size M) a few times but they just don't fit right with my head shape.. I'm going back to using the ear buds.
Bern Outdoor Tech Audio Chips Liner for Bern with Chips - Accessories Unlimited
I can post a picture if needed. They cost $140 new. I'd take $100, but I'm open to trades too. Let me know if you have any questions.