I would contact Johnson Matthey. They are a major supplier of
platinum products internationally. You could probably contact
suppliers like Hoover and Strong as well. I am sure they mix their
own alloys and have at least a contact that they use. They have
always been very helpful to me.
I can’t tell you how iridium works but I am sure it is very hard to
use. It has an even higher melting temperature than platinum.
608 fifth Ave
NY NY 10020
Hoover and Strong
10700 trade Road
Richmond VA 23236
Let us all know how it turns out!