How to anchor coat hooks and shelving in a rock-lath & plaster wall?
Use a neodymium magnet to find studs, they're available online (e.g., Amazon). Some can hold up over 100lbs. They will find your studs. I would not use regular anchors, even though there is sheetrock behind your plaster (that's what sheetrock was invented for: replacing lathe, not plaster. Plaster gave way to a thin coat of joint compound and finally nothing but tape). European countries still plaster drywall (blueboard) as the standard.

You may find the magnets themselves can hold up what you want. Great for hanging pictures as well.