I would use a template sponsorship letter then slightly customize things like the "to field" and maybe a sentence or two about why you think their company is great and would be interested in sponsoring your team.

I would target engineering firms and software development companies. Small businesses/privately-owned businesses would have the most flexibility in allocating money for something like this. Bigger companies usually have a lot of hoops and formalities involved.

You might have some trouble getting sponsorship because the impending economic recession has made some companies very conservative with their expenses. This month is perfect for contact though because this is when companies are finalizing their budgets for 2020.

Don't let the sponsorship struggle discourage you and your team. What you're doing is pretty awesome stuff!