You may try some eucalyptus oil. among its many uses is loosening tight screws and removing rust, so I think it would do the trick. You can get it in a health food store. It lasts a very long time because you only use a tiny bit each time, but it is a natural cleaner. Apply a small amount of the oil to the scissors and let soak in for a few minutes, Then brush with a toothbrush or rub with a rag and rinse until all of the rust is off. Finish drying with a hair blower or out in the sun until completely dry. (Also works great on removing glue from labels on glass, etc--I use it on my car window to remove last year's stickers.)