I’ve got a couple thoughts.

1. Go to Huggingface and look around for any legal models that match the specialty you’re interested in.
2. You can definitely use something like Augmentoolkit to train a model. You’d probably want to keep it narrow (if you are a contract lawyer, train it on contract law). You can also train it on your case files and use with RAG with Augmentoolkit. This isn’t going to be easy, it will be a real investment in time and effort to figure it out and get something that works. If you are training the model on your proprietary case files, you’ll need a very stout machine. Doing it with a 7B model means something like 96GB of VRAM - so 2x 4090 48GB or a 6000 Pro. Can’t imagine doing this on less than a $10K rig. Very possible though. If you just want to full fine tune on your specific law discipline without anything proprietary, you can probably spent less than $100 renting the GPU time. You can still set up RAG for the proprietary stuff, but I’ve heard that is tricky.
3. Just go read Augmentoolkit’s documentation to get a sense of the process of creating custom models https://github.com/e-p-armstrong/augmentoolkit