I've not found any models for bollards, but I do use the Traffic Pylon and Trash cans from the Street Scene as representation from this: https://developers.arcgis.com/javascript/latest/visualization/symbols-color-ramps/esri-web-style-sym...
There's also attempts to do this in a custom setting here: https://community.esri.com/t5/arcgis-online-questions/3d-cylinder-objects-much-larger-diameter-when/...
Cody