Sarah, you're welcome
No, I don't know of one, though I'm sure it would be very seriously over-subscribed; I'd be first in the queue. I imagine if you had a novel professionally edited the editor might be willing to help - the trouble with synopses is that it's hard to be really helpful without knowing the work.
Miss Snark's blog is great on synopses - she actually takes some apart bit by bit. I learnt a lot.
http://misssnark.blogspot.com/
Emma