I did find one, although it comes from China so you're probably best off using the description to find something similar closer to you.
https://www.newegg.com/global-bargains-a13061700ux0957/p/0Y1-00F0-03NU8?Item=9SIA4SR1WV0898&Description=2.5mm to 3.5mm adapter&cm_re=2.5mm_to 3.5mm adapter-_-9SIA4SR1WV0898-_-Product
Different supplier:
https://www.mycablemart.com/store/cart.php?m=product_detail&p=5790