I kinda agree, its highly unlikely someone would just HAND over their unused dream fastpasses. Your best bet would probably be looking on ebay or craigslist.
As for the Dream Fastpasses, its really varies by CMs. Im sure they hand them out with a limited # knowing that people use them at random times, so its likely that if the Fastpass line becomes too long, they MAY not let you through.
Though i cannot confirm, but i recall you cant use a regular fastpass the next day, they simply would say no, but i may be incorrect.