Many breeders do sell to other breeders. They might use breeder forums, Facebook groups, and other breeder contacts. Being part of a breeder club (usually a local one) helps as well as national breed clubs. Some will sell at shows as well.
Most breeds do have a website. Even if it is not updated on a regular basis, it can at least have your contact info and what breeds you have. If someone is interested in a rabbit, they can contact you to see what you have.
There are some that might use classifieds sites like Craigslist or Kijiji to advertise. This can be more of a last resort for some and is usually only pet rabbits rather than breeding stock, but there can be anything listed on those sites.