I've used the services of many mentioned here, including a few highly regarded and respected gunsmiths some keep bragging about. Only once was I truly impressed by a hot bluing job, and that was by Chris Griesbach. His work is worth every penny. Rust bluing? I have yet to find somebody that can emulate the work done over 100 years ago.
What are you looking for to emulate 100 year old rust blue? I have had tremendous success rust bluing, but not sure what made you unsatisfied with what you have had done.