Hello Jim, I wish you find that caramel marble, It is indeed a great plant, and as far as I know, very stable variegation, you do get few plain brown leaves, but all the cuttings I ever made I have never got any reverted one to a totally plain brown "Pluto".
I wish I can help you, but I can't sent living plants abroad although I really do wants to for trade with other gardener from another country
and just want to say, I don't think there are seeds for this one, not even seed for Philodendron "Pluto", the non variegated one and if anyone offer you a seed of a hybrid Philodendron, let alone a variegated one,.... I really wish you will abort the option, your only option is a cutting
I wish you a good luck...
and just to encourage you... I wish to send a picture of mine