As a matter of policy CLR object source code must be submitted to me prior to deployment. With sufficient lead time to review it. And I have access to the source control system.

Depending on how it was deployed a copy of the source files may have been deployed into the extended properties for the assembly. But this is not for certain and I would not count on it.

Unfortunately SQLCLR is a blackbox from SQL's perspective. So you have to be proactive.

You could probably read the bytes out of the system tables and run them against a decompiler but it wouldn't be pretty.

CEWII