How can I find a list of my co-authors for a grant conflict of interest?
As with most other administrative data, it's far easier to maintain this information than to rebuild it from scratch every time you need it.

Maintain a spreadsheet with a complete list of your collaborators, including name, affiliation, ORCID, contact info, and most recent collaboration date for each one.  Keep this spreadsheet in the same directory where you maintain your CV.

If you're lucky enough to have lots of collaborators already, setting up the initial spreadsheet will take significant time.  Better to invest that time only once.

Every time you submit a paper or grant proposal, spend 5–10 minutes adding any new collaborators and updating your information for collaborators already listed.

Each time you need to submit a list of conflicts, extract the collaborators recent enough to create a conflict, in the precise format the agency requires.  Different agencies define conflicts differently, so if you plan to submit proposals to more than one agency, I don't recommend removing anyone ever.

If your agency is like NSF, it will require a list of names and current affiliations of your recent collaborators.  So every time you submit a proposal, you need to double-check that everyone's listed affiliation is current.  A list of affiliations at the time of your collaboration, no matter how you obtain it, is not sufficient.  People move; your conflicts follow them.  (People also occasionally change names, but that's must less common.)