Sound FX CD's is where you should be looking. Hollywood Edge and Sound Ideas has a couple of the largest selections available, but is probably a bit overkill for what you're looking for. Another thing you might try is to rent a video and record the horse and carriage noises, to steal and chop up the effects you're trying to achieve. I think something like Sleepy Hollow, or that other new movie that portrays the story of Jack the ripper...damn forgot the name...but those should have a lot of horse and carriage noise without any dialog on top of it.