Begging your pardon, but if you want to be a lawyer, why are you bothering with a Master's Degree?
But if you are set on your decision.... get your grad school things squared away. When you are ready to apply to law school, get your LORs for law school then. Keep in touch with your professors-- send a Christmas card, an email to check in, etc. Maintain the relationships. You may also end up with profs in your Master's program who will write you LORs for law school.