heartbeat artifacts can be fairly reliably detected from magnetometers. See this tutorial section and the ch_name parameter of find_ecg_events(). You’ll also notice in the ICA tutorial that one of the output boxes says Reconstructing ECG signal from Magnetometers.
Blink artifacts can be detected by using one of the frontal EEG channels as a surrogate EOG. You should examine your data to see which channel has the most clear/obvious blink response in it, and pass that as ch_name. Beware though that this can inadvertantly remove brain signal, especially if the blink detection algorithm does a mediocre job of aligning to actual blinks, so be sure to plot the artifacts to make sure they look right.