You will need a sample of the old finished trim and a couple of sample boards of the new wood. The old sample board will be a reference while putting sample finishes on the sample boards of new unfinished wood.

Now take these sample boards to your local paint store, not a hardware store. At the paint store you can either get a suitable stain/finish of the shelve and test it or have the store work with you to get a custom mixed stain.

The only acid wash used on wood I'm aware of is used to lighten wood prior to staining. Without a picture it is impossible to say what type of stain you will be dealing with. The employees at the paint store will be able to help you out.

Make sure to test each possibility with a clear finish coat on the sample boards before committing to the project.