I remember seeing a ton of factory workers every time I passed through Shulin Train Station. In and around Kaohsiung Train Station was another one.
Traditional markets might work. I always see a few Indonesian guys at the market in Shuidiliao, Pingtung County. I think they’re housed somewhere in the area, and they probably work in the Pingnan Industrial Area nearby.
Then there are the local businesses (Vietnamese restaurants, Indonesian restaurants, related grocery stores) that cater to that community.
Sometimes the local Foreign Affairs Office organizes activities or Chinese classes for new arrivals. As a foreign resident you are also eligible to attend these classes. If you’re new to the Chinese language just don’t expect to learn much. From what I’ve heard they move at a different speed.
And this has nothing to do with anything, but many of those Vietnamese moms are FINE. Interviewing them sounds like an extremely pleasant activity.