Our big gates came from Drs. Foster and Smith, online. They are metal, 40 inches tall, and have a tiny gate at the bottom for smaller pets.
The mounting hardware is a flimsy plastic cap, so hubby attached the gate to the wall with plumbing strap. If you get two and mount the bottom one right-side-up and the other upside down, you can cover almost the whole doorway.
The only problems we had with it were that Zita liked to chew on the bars and once got her lower jaw caught between two bars. I had to grab her head and turn it to get her loose. She didn't try that again. The other problem is that there is a gap between the gate part and the frame large enough for Sparky Chihuahua to fit through.