DD's softball team allows for company sponsors for the individual player or team to help cover cost. Are their certain companies that you look for to sponsor? Seems as though bigger companies don't sponsor. Maybe target smaller companies?
For high school ball we target local restaurants, and other merchants that are in close proximity to the school. I have also had some luck with people who I deal with personally - insurance agent, investment advisor, mechanic.
Sporting goods franchises and stores will often help local youth organizations. Dicks used to have a program set up just for that, not sure if they still do. We used to have the best luck with local stores or restaurants by asking them to donate goods or gift certificates and then we’d raffle them off.
Sponsoring individuals raises some red flags. I’d be careful with that to make sure it doesn’t affect HS or college eligibility.
The best companies are the ones that are run by relatives, close friends, or people who are indebted to you. However, I would be somewhat cautious when soliciting some companies since in return for their generosity, some day and that day may never come they may call upon you to do a service for them. So steer clear of companies such as the Genco Olivie Oil Company, International Immobiliare, Barone Sanitation, Satriale's Meat Market, and other "family" businesses. Then again some of the relationship you build may help when dealing with uncooperative colleges or poor umpires.