go to Otto gasenginework in MD, Dave Reed.vry good with caerpillar.I don't know if he's listed on bb or not but you can find him on smok stak Gene
I have had good success getting ahold of these people with quick turn around at a reasonable price!
Niagara Piston Ring Works in Corry PA
Guys have said that Hastings still make rings for some of the old CAT engines also.
Otto: http://www.ringspacers.com/
Niagara Piston Ring Works Inc
18455 Sciota Street
Corry
PA 16407-8937
Phone: (814) 664-9233