The trouble is rescues get quite attached to the buns they rehome so if something goes wrong they like to take the bunnies back. Plus is the rescues doesn't personally know the local rescues to you then they may not feel they can rely on them to provide the same support - I'm sure your aware rescues vary in their advice/standards
Is it a particular type of bun your looking for? If your local rescues don't have anything listed its often worth paying a visit to see what they haven't put up on the web
Tam