I believe type R,S, and B all contain Pt. Type s is like 98%platinum and 2% Rhodium. I use Type S at work. The semiconductor industry uses them a lot. They do occasionally go bad. I cant seem to find anybody in my area that uses them but me. local Foundry uses K type. I would try semiconductor bone yards in your area if you have any. They are mostly out west. If they know what they are you wont get them cheap. Also, generally the companys that sell them will buy them back for the wire when you purchase new ones so most companys dont just throw them out.
John