I've heard that model agents like a large jawbone: is there a way to increase my jaw?

Larger Jaw. There are several ways to increase the dimensions of your mandible (lower jaw). Perhaps the easiest and least invasive method is by inserting custom-designed implants under the soft tissue in the areas you want to bulk up. This is a relatively simple procedure, usually with little down time.
Jaw. Yes. By having genioplasty or orthognathic surgery. But the dimensions should be in harmony with rest of the face.