Where do I find Webform CiviCRM module for D8?
Two options: 

1) look for and download the 8.x-5.x-dev version [this is updated every couple of months/I will try make that weeks]:

https://www.drupal.org/project/webform_civicrm/releases/8.x-5.x-dev


2) or check out the 8.x-5.x branch from the GitHub repo to always be on the latest:

git clone https://github.com/colemanw/webform_civicrm.git --branch 8.x-5.x


and then:

git pull