My 87 year old mother

Question

My 87 year old mother just bought a new Maytag over-the-range microwave model MMV1153BAW. The bolt that came with it is too short to install it into her cupboard configuration. She says it is a #6 metric bolt, about 4 inches, and she needs one about 5-1/2 inches. She's gone to hardware and big box stores and they don't have any that are long enough. Can you help? Thank you!