We tried to hire someone senior for 8 months before giving up and just grabbing a junior dev that wanted to do infra stuff and trained him up. I have worked at shops with people like you describe but it seems they're all happily employed.
[1] Not whiteboard style, on their own time, on their own computer, not timed or watched. They can take a week for all we care.
I have no idea how you could find true experienced sysadmins in your case. They exist though, that much I can tell you. I have 20 years of experience, I write bash, python, perl and lately mostly go. I am not a greybeard as I am just old enough to have been a junior for the greybeards that wrote linux kernel patches among other things to solve infra problems.
I have led Ops teams in one shape or another for about 10 years. I second that having a junior dev do Ops work without supervision will not bring joy to your life, mostly because they do the darnedest things! One of the trainees here decided to remove a ControlTower guardrail from a root account, for a personal experiment in a sandbox; then three weeks later created a public S3 bucket in a production subaccount and leaked a bunch of data...
90% of developers just don't have the mindset for Ops work.