There are a few ways you can find a manufacturer for your brand.
1. Find a local manufacturer. Get in touch with a local manufacturer and start to see and understand the process of how garments get made.
2. You can contact local pattern makers, pattern graders, pattern cutters to get your garment made and even a sewing machinist. There is a lot of trial and error at the beginning but you will find your rhythm and start to get more familiar with how things work.
3. Google and Youtube. There are thousands of manufacturers around the world. It's no secret that majority of brands get their clothes made in China. I'm not going to give you the direct answer just for the simple fact that it is literally right in front of your face and you're not doing anything about it except complaining to others about how hard it is to find a manufacturer.
All the answers are at your fingertips, it's just a question if you want it bad enough. Clearly if you're giving up because you can't find a manufacturer or a brand on Instagram won't reply to you asking what manufacturer they use then maybe this isn't the industry for you if you're looking for quick and easy answers. Don't start a brand if you think it's the easy way to make a buck or become rich, trust me you won't last very long. There is millions of brands out there that sell t-shirts, why should they buy yours? Please don't say it's because we're different or we are for the people or this is for the crazy ones. Put some real thought into your brand.