Don't ask a factory to make 50 pieces unless you know them. Instead, buy blank garments and have a local shop print them, source vintage clothing to rework, or hand-sew pieces yourself. These are the only realistic ways to start small.
Chapters
So someone wants to start a clothing brand, but they only want to order 50 pieces. What's their best option? I would never recommend going to see a supplier and telling them, "I want you to make me 50 units of this," unless they are your best friends or they owe you a lot. If you do that, chances are factory is doing some really sketchy stuff. There's no chance they're making any money off of it. The best way to start is with blanks or with repurposing vintage clothing. And I understand that that's not the nature of every single clothing brand, but unless you know how to sew yourself and you can make every single unit one by one, it's pretty much your only option in order to get very low quantities. With blanks, you can order as little as one, and you can go to a local screen printing or embroidery shop and get it taken care of. With repurposing vintage, you can go and thrift vintage pieces. So I think that's the best way to start off.