There are a bunch of us out here that can send and receive them, you just have to poke around a bit to find the (ever-growing) community. Services like micro.blog and those involved in the IndieWeb will (often, though not always) have support for it. Here’s a short Twitter list of people whose personal sites likely have the ability to send and receive webmentions as well.
So far the only site that is sending me webmentions is @lobsters 🙁
— Cadey A. Ratio (@theprincessxena) December 1, 2020
One of the largest senders is Brid.gy which sends Webmentions on behalf of services like Twitter, Mastodon, Instagram, etc. If you set your site up to syndicate content to those sources and register with Brid.gy, it will send likes, replies, comments, etc. to your site as webmentions. Ideally this is meant to aggregate all the conversation around your posts to your own site.
Are you displaying them on your site as well?
As a visual indicator on posts, I took an extra step to add a Webmention button/badge and a URL field to my posts with a note about webmentions so that people could send them manually even if their platform/CMS isn’t capable of doing it automatically yet. (I don’t have a lot of direct evidence yet that these things help except for edge cases, or when I want to force mentions of my website from my referral logs.)