There is no tool to generate Icons for smartwatch but we do have guidelines to help developers generate proper icons.
You can find more info here: http://developer.sonymobile.com/knowledge-base/tool-guides/download-the-new-smart-extension-sdk-and-create-smart-extras-apps/
Update: The Sony Smartwatch design guidelines are available in Sony Add-on Documentation kit or directly here: http://dl-developer.sonymobile.com/documentation/other/SmartWatch_products_2.pdf