A finger is simple. An arm takes more time and the strain on the body is immense. It is lessened in a medical setting where there are protein supplements and fluids, so there is more building blocks to utilize.
So, yes, I managed a serum based on salamanders ability to regrow their own limbs. It's undergone a military testing phase, but it's not exactly publicly available. Even so, as the creator of it, I can license it out as I please, and have a small amount under extreme explosive lockdown lock and key.
Your ability to do such things is extraordinary. I would like a genetic sample of you. If you are willing. I do not think you can be further modified, but to study what makes you able to do such things would be a great opportunity.