The relevant info in the AnyEvent::HTTP documentation refers to request headers and reads

---
   You really should provide your own "User-Agent:" header value that is appropriate for your program - I wouldn't be surprised if the default AnyEvent  string gets blocked by webservers sooner or later.

---

The server blocks the AnyEvent request, but works ok if you indicate another valid User-Agent. Like

     http_get $url,
              headers => { 'User-Agent' => 'curl/7.47.1' },
              sub {
     [...]
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