proofreading questions for authors

A question for any authors regarding proofing. I've been blessed, or cursed depending on viewpoint, with a blue pencil stuck in my eye. I've proofed for three authors, two of them including me in their acknowledgements. I want to pursue this as a retirement activity and source of revenue. My questions are how do I reach authors to secure the commissions and what are reasonable rates for this work? Any and all input are appreciated.