Chromobacterium violaceum might be worth a try.
Use almost any soil as long as not too acid.
Keep moist and then very carefully place some sterilised rice grains on
the surface. Chr violaceum will go for the high C:N ratio and colour
infected grains deep purple. Carefully remove them and plate out on a
starch containing medium.
Failing that go for Bacillus cereus var. mycoides. In virtually all
soils and unmistakeable in colony form.
University of Raeding, UK>