I think lots of tasks on phabricator can have a project where volunteers can find requests for bot creation, and pickup a task that they want to work on it.
Currently it's hard to sorting this kind of task.
- T165951: Create bot to add copyvio template to pages
- T172944: Request for congratulations bot for users on every 500 edits / 50 kB for Urdu Wikipedia
- T166995: Create a bot to clean old pages of testwiki
- T174528: Tool for displaying a user contribution summary
I found 4 tasks that immediately come to mind because I'm a subscriber. Lots of other probably exist. But we need a tag for this :)