When I looked into it, I found that although you can find organic wood most orchards use pesticides. I spoke to a few Australian suppliers and they said because the wood has to be cured for months or years and as the pesticides used in orchards have very short half-lives it should not pose any health issues but then one that originally said it should be fine came back to me and told me it wasn't suitable and wouldn't give a reason, which was a bit disconcerting.
Just to cover yourself make sure you mention that you plan to use them for your pet rabbit to chew because, under Australian consumer law, goods must be reasonably fit for any purpose disclosed by the consumer.
If you do end up using them, you don't want it to have been kiln-dried, which is often the case with large suppliers and imported wood. Using a kiln speeds up the drying process but leaves the wood flavourless. I'd also give them a clean if they haven't been cleaned before using them to remove any dust, etc.
Bunnies will prefer fresh apple sticks but smoking wood chunks are a great heavy-duty chew. The big chunks will last longer, dried applewood is harder so great for their teeth and the familiar taste they love will incentivise more reluctant bunnies.
They're great to make toys from too and are more readily available, giving your bunny the chance to try wood that they normally wouldn’t have access to.
Common smoking woods that are safe for bunnies: apple, pear, hazelnut, grape, mulberry, pecan, mesquite, peach