Contact coaches directly. Be prepared to sell. Promote your best attributes. Be prepared to defend your negatives. Do not lie. Ask these coaches where you can get in front of them this summer or fall.
If you call you have about twenty seconds to attract interest. It's the nature of a sales call. If you do well the conversation will go further. You will know if you're being blown off.
If you email the coaches you're at the mercy of them returning an email. You don't have a lot of time to lose. It's already July.
Keep in mind a D3 coach doesn't have roster limitations if he chooses not to. The bad news is he can tell you to attempt to walk on in the fall when you have no shot. Or if you walk on and shine he has a roster spot for you.
The objective isn't to just get s uniform and be player #40. The objective is to find a place to compete for playing time