Great question. Happy to have a conversation on this (I currently have a reduced launch rate) and explore your options but here are my top tips.
1) Tailor my advice to your business's niche and obviously look in that area, but for example great cofounders could probably be found as follows
- contact MBA students, many want to start their business afterwards
- contact specifically business schools with an entrepreneurship department and mention that you have a careers opportunity - many have contact details of even their careers team
- join entrepreneurship online communities and ask around there
- call up existing businesses in an adjacent space and ask if their leadership wants to become a co-founder
- use LinkedIn to reach out personally to individuals

Happy to find other options together with you. Best of luck, you will succeed.