Hi there! Yes, the Fire-Lite SD365 is a suitable replacement for the SD365-IV. It’s important to note that they are compatible devices. You can purchase the Fire-Lite SD365 from reputable fire safety equipment suppliers, online retailers, or directly from Fire-Lite distributors. Check with your local fire alarm system suppliers or visit our website at firealarm.com for more information and purchasing options. If you have any more questions or need assistance, feel free to ask!