Hi Mate and Merry Christmas
Option 1:
Your best bet would be Ebay you normally find bip rear subframes going cheap, as for the faring and rear seat again Ebay but hold out, these normally command stupid money, now and again a cheap one comes along.
Option 2:
Its a popular conversion from bip to mono, put the word out on the forums i am sure someone would be willing to swap you, but i would expect a little cash as well.