Where can i find piercings for the ring finger?

My girlfriend's birthday is coming up in September and we both agreed on getting our ring fingers pierced and tattooed as rings instead of having real ring. I can't seem to find a diamond for a piercing on her finger.She is going to get her sternum pierced on her birthday and I thought it would be the perfect time to propose and go ahead and pay for the piercing on her finger! I was wondering where I could find a diamond to pierce in her finger and how much it generally cost's to get it done. Please help because I really want this to go perfectly!.Thank you so much!