I believe by Mindanao Gum, you mean Rainbow Eucalyptus, Eucalyptus deglupta, try an internet search on "Rainbow Eucalyptus", you should get results for seed or young seedlings. I don't think there are many ''mature'' or well developed as bonsai E. deglupta in North America. It is a relatively recent introduction to North America. It is a tropical tree, does not tolerate much in the way of frost, so shipping to Michigan this time of year is risky.
I know of one seedling, now about 8 years old, being trained as bonsai, it looks like with time, it will be acceptable as a species for bonsai.