Sites currently using webmention.io to receive pingbacks on their behalf:
Accept webmention and pingbacks for any site by adding a simple html tag
<link rel="pingback" href="http://webmention.io/username/xmlrpc" /> <link rel="http://webmention.org/" href="http://webmention.io/username/webmention" />
Converts Pingbacks to WebMentions
You can use webmention.io to handle Pingback requests and send them to you as a webmention.
To use, add an html tag like the following, replacing example.com/webmention with your own webmention endpoint.
<link rel="pingback" href="http://webmention.io/webmention?forward=http://example.com/webmention" />
How to Use
If you want to use this right now, get in touch with aaronpk and request a demo account on his instance. While not yet a production service, it has an API that can be used to query a list of mentions for a site.
You are more than welcome to use the pingback->webmention conversion service as described above. Or you can install this on your own server from the source code on Github.