It's not particularly obvious, but you find a release for which `has_sig` is tru...

It's not particularly obvious, but you find a release for which `has_sig` is true then you take the URL from that release and append `.asc` to that URL.

  $ curl -s $(curl -s https://pypi.org/pypi/cryptography/json | jq '.releases["2.2.2"][] | select(.has_sig) | .url' | sed -e 's/^"//' -e 's/"$//').asc
  -----BEGIN PGP SIGNATURE-----
  
  iQEzBAABCAAdFiEEBf2foWz3VzUNkaVgI1rl8Sn57ZgFAlq6dNgACgkQI1rl8Sn5
  7Zg0Ygf/WzulfXom9qdbCHrUJh2xkTxPqK2/SUqDqOQ1OdKJm+MxDBcMhwrCdBDh
  8+eXyPTLnnhPUcCSqVFcJeUu9KyKB2MhKi7gdBUHrDxjbufexxPC+L/KwjOq3nod
  gL4OPHGGeX2ZgSlwFPR4zPIIheUmf9kPX88qtW8DD8zmuyhci6ibac9a/3fHkDVt
  H27B+aqs+WObMjcfwZV7gMnRbZwUOBZvVFRxwfMHVuMpfbwhQC8HdBK74XKNaoTd
  Golmpa5fqRm1sNquBz9YRVElWuw1qj1CZJhRBuR7V5xyPLX8J7EVUrYa70/fVtfr
  hW7oAlNbMFYb58hGC9K20v6WX8XT2w==
  =zox2
  -----END PGP SIGNATURE-----

At least that's what I was able to piece together from the docs...