Vendors for platinum and palladium?

Hello all, I have just started to get back into all of this, I had
taken a jewelry/metal smithing class about a year ago and dropped out
half way threw because it was to difficult to go to school and work
at the same time. Ever since I have had a bad urge to get back into
all of this and finally put my foot down a few weeks ago and started
buying my supplies. I have never worked with platinum or palladium
but I would like to start, does anyone know a good vendor for these
metal ? And any tips on working with them, I have only worked with
Sterling silver, copper, gold, nickel… Im looking for flat stock
platinum / palladium …

Michael Woltmann