I've bought 100's of yards of fabric from ebay sellers. That's a great place to start. If you need to get it out of the garage in a hurry, you might rent a storage unit for awhile until you can get it all in order or see if someone in your neighborhood could store some of it for you. Another thought: bundle it in groups of fabrics that would make a nice quilt. One word of warning though: don't sell yourself short. Just as today's fabrics are now selling for $10, your fabrics have increased in value also. Don't feel like you have to sell it for $2/yd just to get rid of it unless you're in a real bind for money. If you have as much fabric as you say, it will take awhile. We have a local newspaper that posts classifieds on their website for free. It's been so successful that the classifieds in the newspaper have dropped down to nothing. You could also put up eye-catching signs on bulletin boards - library, grocery store, senior center. If you're not talented in creating a poster, I'm sure there is a young person nearby who would like to help you.
Good luck! If you decide to sell on ebay, be sure to give us your seller id so we can look over what you have. And...good photos will sell your fabrics for you so be sure to spend time on them.