If your headphones are out of warranty I would look at a store on amazon called Wicked Cushions. I had the same issue with a pair of Bose headphones I bought a pair a replacements and they were just like the factory cushions and easy to swap out. Not sure what beats you have but here is a replacement pair.
https://www.amazon.com/dp/B01F4GJ2RQ/ref=cm_sw_r_cp_api_ihIyBbB73A4F4
If you want to get new ones you can buy them on amazon and replace them yourself, pretty easy, did it all myself. Just needed something to pry the old ear cups off and then stick the new ones on
Wicked Cushions Upgraded Beats... https://www.amazon.com/dp/B01F4GJ2RQ?ref=ppx_pop_mob_ap_share
A little thicker than the stock ear cups, but very comfortable. Includes a card with a link to a how to video on YouTube