I have long-term relationships with most of my sponsors that take time to develop. it is very unlikely to get any paid sponsorship for your first major adventure. So, do a big thing and then ask companies to help for the next big thing not the other way around. Sponsorship is also not a charity, so think in terms of what you can do for the potential sponsor. Be creative if you don´t have a big reach, you might be able to help with blogposts, products testing or sth. similar.