My CP does sponsor letters every year and usually does a very good job getting support. She does a separate letter for family and friends and then for the businesses that we patronize. We begin each year with a list of those who have sponsored her in the past and include them in the list for this year, but try and think of new sponsors that can be added. The letter goes on the gym's letter head-I make copies, and her gym has a sponsor letter explaining what being a sponsor means (ie how much it costs to be an all-star cheerleader and how their sponsor donation will help) so I include this with her own personal letter.
In her personal letter, she talks about herself and what her last season of cheering was like and then gives a run down of what her competition season will be like this season. She then explains that by being her sponsor, their donation will assist her with the expenses for competition fees, travel expenses, and uniform and apparel costs, and how much she would appreciate their support.
She thanks them in advance (she will also send out personal thank you cards when she gets notified that she has received a donation) and explains how they can donate online or how to send their donation to the gym to be entered in her account to be used for gym-related fees. I include a picture of her, either with the letter, or sometimes when I make copies of the letter head I take a picture and make a stationary-type of paper out of it by copying a picture of her in her uniform on the paper and make color copies. She mails the ones for family and friends and those patrons we have visited recently, but will personally hand them out to new ones. Examples of sponsors she has received donations from are doctor, dentist, hairdresser, councilman, labor union-my husband's, insurance agent, local pizza joint, local merchants like t-shirt/embroidery store, local bars, local restaurants, city athletic departments, small mom and pop shops-basically take a look at small shops that would sponsor a local baseball team; they are your best bet.
Sorry this was so long-I guess I should have done this with a PM, but now others can see how she goes about receiving sponsors for her cheer expenses. GOOD LUCK!!