^^^
Exactly. Even if he had a rich relative who understood college/pro tennis very well, they just wouldn't give money to the OP. He's 18, a legal adult in the US, and if he hasn't shown promise by now, nobody will want to "sponsor" him.
Parker, tennis is not all about people giving stuff to you. You will not get free equipment, coaching, and other neccessities from sponsorships if you cannot play. Nobody is going to give you things, and sponsorships are not the point of tennis. Winning matches is the point of tennis in a competitive setting, so for now, forget about the sponsorships. Make your name in tennis not through sponsorships but through your game and hard work, because nobody's going to give you things. You have to work for it.
OP, how long have you been playing? A good training regimen alone cannot guarantee you ATP points. There are many intangibles-mental fortitude, understanding of the game, knowledge of the opponent, tenacity, and most importantly, experience. Not everybody has what it takes to make it on the tour. Even Devin Britton, who plays D1 college tennis and won the NCAA title in 2009, is floating around 800 right now. What are your goals for tennis? How long have you been playing? It's not going to be an easy ride, but I sincerely wish you the best of luck with your goals!