For a business look you might want to try pencil skirts! They're perfect for that type of event. If not, just go with dress pants. For the top I recommend a blazer because they are very professional. You can go to stores like Nordstrom, Nemain Marcus, Macy's, or even Khols.
♥ Hope I could help, and good luck! ♥
go onto Cafepress.com. you can customize t-shirts and have people buy them online, and i believe you can order them so you can sell them in person. also try vistaprint, they have business cards, shirts, lights, keychains...etc that is customizable