Desde a versão 7.34.0, o Curl tem as opções --tlsv1.0 , --tlsv1.1 e --tlsv1.2 para essa finalidade.
A página de manual diz
-1, --tlsv1
(SSL) Forces curl to use TLS version 1.x when negotiating with a remote TLS server. You can use options --tlsv1.0, --tlsv1.1, and --tlsv1.2 to control the TLS version more precisely (if the SSL backend in use supports such a level of control).
...
--tlsv1.2
(SSL) Forces curl to use TLS version 1.2 when negotiating with a remote TLS server. (Added in 7.34.0)