The 3.5mm AV cables use an older analog video signal format. HDMI is completely digital. As you may have already noticed this is a problem, because no device outputs this analog signal, only HDMI.
So, if you want to use this projector, you're going to have to convert the only output you get (HDMI) to the older analog signal. The converters are active devices, which means that they're expensive and probably require their own power supplies.
I highly doubt there is an all in one MHL to composite video converter.