Is there a way in Ubuntu to find community written Lenses? Something similar to https://extensions.gnome.org/. The Ubuntu Software Center would be a good place in Ubuntu!
Ideally, all community-written lenses should be submitted to the Ubuntu Software Centre, so that users can benefit from them.
The process to get them in the Software Centre is really easy, so if you see any lens that might be worth making available to millions of users, the best thing is to point developer to how to publish them:
What lenses for Unity are available? provides a list of most lenses that I've heard of. If you would like to follow development more closely, I'd recommend looking at this Google+ profile: https://plus.google.com/104126327661540805262/posts. I believe OMG!Ubuntu plan on creating a repository for lenses (Source: Will there be a place for example a website or a PPA that holds all the lenses for Unity?). In Ubuntu 12.04, you may be able to find lenses within the Software Centre itself (source: http://www.omgubuntu.co.uk/2011/10/unity-integration-to-run-deeper-in-ubuntu-12-04/)
If you would like to create your own, you may consult either:
Try this blog. It has enlisted almost all the lenses for Ubuntu. you will like it. List of All the Lenses for Ubuntu