It's a Ford stock E450 seat. Should be tons out there.
I know JC Whitney carries them...but my "go to" is always Amazon.com They seem to have everything...shipped right to your door.
PLEASE do not send questions via Private Message, my inbox fills up too quickly. Post questions in the forum as a new thread so that other users can benefit from the answers. Use Private Messages for sensitive information only (VIN, Contact info or things you do not want the public to see).