My wife researched and ordered a dirndle from Amazon that is considered legit. Then she knew ahead of time if it fit. She also reserved one at a rental in Munich. She liked the one she bought better and didn't take the rental. Hers was slightly more ornate.
I bought after I arrived. I found a department store that is only Bavarian clothes.
https://www.daller-tracht.de/It wasn't cheap and I bought in the lowest tier. It was still 290 euros for the lederhosen plus the same for a vest. Add a couple of shirts and the long socks and it was pricey. I brought my own leather boots. Plain white sneakers are also acceptable with the appropriate socks.
Worth every damn penny. It was a blast. My hands were sore from operating the buttons, and you want to practice disrobing to piss because those button holes take a while to break in!
If you can swing it, it's part of the experience to buy in Munich. Basic but real lederhosen are worth it if you think you will return or will wear them to stateside if festivals.
We went for the first time this year and I'm happy to answer questions!
Staff - take out the trash.