How do I find a business partner with a 50% partnership?
All business partnerships should be based on each partner bringing something of value to the partnership.
Basically without this person, the startup would not be possible. So first ask why you want or need this person as a partner? The reasons I have always partnered were because someone had the expertise, a skill, could fill a key role, had the experience, provide capital, and or had time I did not have. So once you know why you need a partner you begin looking for someone who can fit the need.