Looking for a ring replacement for my cage

Hello!
Im new here and recently started exploring some self locking as i always was curious about it. I bought a cage off of amazon and it was fine at first. The problem i have now is that the ring is slightly too small. It has a 5cm/1.9-2inch diameter but i need one with 5.5cm/2.1-2.2inch or 6cm/2.3-2.4inch. The only problem is that i cant find anywhere where i can just buy a ring and dont have to buy a whole new cage. If anyone could help that would be highly appreciated. The cage is called: Male Chastity CB-XL on amazon but i will add a picture of the ring aswell.

 

I have worn it for a couple of days, and its mostly fine. Just whenever im lying in bed and try to sleep does it become a problem. Maybe i also doing something wrong, but i start getting a slight burning/painful feeling at the bottom of the ring after like 5-10min of being in bed. Its mostly only when im lying on my side but also comes on my back after some time longer. I tried putting a thin cloth over the metal piece, thinking that was the problem but it didnt help either.