I was searching for the specific lddh350aa75 firmware and was getting frustrated with sketchy third-party sites. This link provided the exact .bin (or relevant file type) for my device.
dfu-util -a 0 -D lddh350aa75_firmware_v2.1.bin -s 0x08000000:leave lddh350aa75 firmware link
Instead of searching for “firmware link”, search for: I was searching for the specific lddh350aa75 firmware
Look for any line containing LDDH or 350AA75 . lddh350aa75 firmware link