Most Wishbone bushes can be replaced as Dazza has said, the only problem is if the wishbone is worn or corroded the bush will not sit in place tight enough and can come back out whilst you are driving.
Most garages now wont replace just the bushes for this reason, they will only replace the complete wishbone assembly complete with new bushes already fitted.
Most wishbones are now "Pressed Steel" therefore not too expensive to replace.