Replace / Repair Diamondback bike stem
From the information available your bike uses a 1-1/8" quill style adjustable stem. The only other pertinent  variable is handlebar diameter. While you most likely have 25.4mm (1 inch) bars you could have 31.8mm bars. Locating replacement bolts will likely be difficult as the pinch bolts of pivoting stems are typically brand specific in terms of length of the shoulder and diameter of the head.