There are many different ways to fund a community garden. You can have dues, do fundraising activities, such a seedling sales and such, or you can even apply for grants.
There are national grants from large organizations, such as National Gardening Association, Home Depot, Fiskars, etc. Local governments, businesses and colleges sometimes offer grants, as well. These sometimes have specific requirements, such as gardens in schools, location in a low income area, etc., but there are many too choose from, and there is probably something that will work for your group.
Sometimes you can get donations, as well. Tools, fertilizers, seeds, etc., can be gotten at a discount or free if you are willing to show the company as a sponsor of your garden. This can be as simple as a small sign at the garden, or including their information in all your marketing materials, including your web site if you have one.
So check around, there’s probably some help in getting your community garden started.