Why not start by asking one or another of the authors (on the site) who's writing you like. (There's probably a reason you like them!) MANY will be too busy and/or not feel qualified to edit for someone else (Don't be offended if they say no!). Some may not have time but can recommend someone that's helped them. And, a few might even be willing to give editing a try for you.

Whatever route - a volunteer here or your asking. I recommend you send anyone you'd like to edit for you a few pages of your work - for a "test" edit - to see what kind of an editor they are. There are almost as many styles of editing as there are editors. You want one you can work with!

Best of luck,
Anne