I can't tell what type of bottom bracket it has. If it is the older, but common "square taper", then it may not be too hard to find a replacement left arm, that will fit, even if a different brand. You need to measure from the center of the pedal axle to the center of the crank axle to get the length. Common sizes are 165mm, 170mm, 172.5 mm, but a bike like yours may have a less common smaller size.