Where is this?

Any city that has proper suburban shops, strip malls, or Chinatowns. Avoid anything on Main Street. Look for small hole in the wall proprietor operations. This is one of the few times where economies of scale doesn't make things cheaper so avoid any big brands.

Also, watch a YouTube video or two to get a crash course on fabrics. In the states it's labor that's expensive but the fabrics are usually genuine. Alternatively you can go to South East Asia or places like Hong Kong and Japan too but there's a higher likelihood of fraud when it comes to the fabrics. Labor is about a magnitude cheaper though.

Bring your own fabrics if you want authenticity. Fabrics are cheap (relative to the cost of a nice suit on a tech worker's salary)

Another suggestion (not advice, I am hardly a professional when it comes to tailoring) is to commission more cotton clothing first to start so you can get a feel for the process. Suits are nice and all but are an investment of time and money and need constant dry cleaning. Try some custom tailor daily wear instead of H&M for a change (better quality and contributes to your local economy).