The I attribute only exists on matrix objects, not ndarrays. You can use numpy.linalg.inv to invert arrays:
inverse = numpy.linalg.inv(x)
Note that the way you're generating matrices, not all of them will be invertible. You will either need to change the way you're generating matrices, or skip the ones that aren't invertible.
try:
inverse = numpy.linalg.inv(x)
except numpy.linalg.LinAlgError:
# Not invertible. Skip this one.
pass
else:
# continue with what you were doing
Also, if you want to go through all 3x3 matrices with elements drawn from [0, 10), you want the following:
for comb in itertools.product(range(10), repeat=9):
rather than combinations_with_replacement, or you'll skip matrices like
numpy.array([[0, 1, 0],
[0, 0, 0],
[0, 0, 0]])