Looking to Assistant Direct (or something like it)

I've recently completed my masters degree (in vocal performance/opera) and I'm looking to get more into directing (opera, musical theatre, straight theatre).

I know "assistant director" isn't something I can find on or apply to via a job board. Of course I'd ideally like for it to go towards my 'career' but if it's more likely for me to get a role volunteering I am open to that as well.

I don't even know how to get started or where to look. I've cold-emailed a few theaters/companies here and there and from the ones I've heard back from it's mostly been a "thanks for reaching out keep an eye out for future postings" type of thing.