I would highly recommend Pequea Carriage Shop. They're in Lancaster County, PA but I think they can ship all over the USA. I've had several of their carts and they've all been well balanced and durable. They have a website but they're Amish so if you ask for an email you'll get a scan of a hand written note. I own a Meadowbrook (my first mini cart - 20 years old and still in use). I had the springs replaced with heavier ones. This is the cart I used for axle draft experiments. I also put sleigh runners on it one of the few times we had enough snow for it. I have had three road carts, two stained, one painted. And they made a cute show cart in blue to my specs.
I would not recommend brakes on a two wheeled cart because when you step on the brakes the shafts are forced down. You can learn to use them but it's tricksy.