I don't know where you could find one: they were discontinued around 1996 so it would have to be a second hand one. Prices could run from $500 to $1000 for a decent one.

Why not try posting a wanted request over at the Jemsite or Talkbass forums? I have seen a couple of posts on Talkbass where people have asked for SR1305s, and some have been sucessful.

Good luck, I hope you get one!