Several sites provide easy ways to get CVSS scores. Several of the major ones are listed below.
NIST NVD site has all alerts CVSS scored and presented at the below URL
They also have XML feeds that anyone can use
ISS and X-force CVSS score all of their alerts
A link to Tenable's vulnerability checks is :
Browsing a plugin reveals a CVSS score when available; eg,
Information-Technology Promotion Agency, Japan
BRI Business Risk Intelligence GmbH CVSS V3.0 Calculator