How to get paint to adhere to plastic items?

Plasticote might be what you are looking for..........

Use Chalk Paint, I painted my plastic tissue holder, a silver tea pot, 2 plastic serving trays, it is brilliant. Then I used crackle for an added effect! Watch Youtube videos about chalk paint, amazing product.

Spray paint the item with Rustoleum for plastic

I use either RustOleum or Krylon spray paints that are for plastic (they have multi-surface spray paints that include plastic). Here's some info on painting plastic: https://www.bobvila.com/articles/how-to-paint-plastic/#.WoGcYKinFPY

I believe Rustoleum makes a spray paint that works on plastic

You need to sand the plastic item first. This gives whatever paint you choose something to hold onto.

Lightly sand then paint with gripper primer then paint as you wish.