cpython/Lib/test/certdata/secp384r1.pem

$ openssl genpkey -genparam -algorithm EC -pkeyopt ec_paramgen_curve:secp384r1 -pkeyopt ec_param_enc:named_curve -text
-----BEGIN EC PARAMETERS-----
BgUrgQQAIg==
-----END EC PARAMETERS-----
ECDSA-Parameters: (384 bit)
ASN1 OID: secp384r1
NIST CURVE: P-384