Here is a link to a USA supplier of magnets that will work with the metric screws on the back of the BrewPi Spark V2.
https://www.kjmagnetics.com/proddetail.asp?prod=MM-A-16 -
They fit well - M3 size screw with a tapered countersunk hole.
Just remove the screws on the back and then screw in these magnets.