You can still do it. Here is what I would do:
Get a letter from the doctor who will provide the vision therapy that explains exactly how much it will cost and why your son needs it and how it will help him.
Then set up a day and time for a fundraising dinner. You can either use a church and get people to donate the food and to help you cook it or you can consider finding a restaurant that hosts fundraisers. For example, I know that Mimi's the restaurant does them. Once you have that set up then you can approach some small or medium sized businesses to help you by donating auction items. You can just walk in and show them the letter and ask if they can donate anything. You could also collect gift certificates. Another idea is to contact anyone you know who has a direct sales business like Mary Kay, Tupperware, Pampered Chef, Avon, Scentsy, etc and see about having them help you do a fundraiser. Most of these companies have a fundraising program and you can make quite a bit of money with these. You could do it as a separate fundraiser, or you could have 3-5 of these reps come to your dinner and sell products and then donate a portion of their proceeds to your fundraiser.