These days, ChatGPT is a good tool to find competitors so long as you are descriptive about what such a competitor does as their core business. I find that if ChatGPT gives me a list and they are all real competitors, there are likely more, so I simply ask ChatGPT to produce more until those competitors I find are not so relevant.

Another, more tedious way is to pretend to be a customer searching for such a service, whether you are on Google, social media, etc.