Welcome soulhawk!
I am not familiar with this particular dahlia. But you could try Swan Island Dahlias www.dahlias.com If they do not carry it they may be able to help point you in the right direction. Also Old House Gardens carries heirloom dahlias. Again, not sure if they have this particular variety but they are very helpful.
May I ask if you specifically must have Periton or would something that looks similar do?
Oh, and I wanted to add that we have a Dahlia forum here. You may want to post there to see if any members have Periton and where they purchased it.
http://garden.org/forums/view/...
