sadpanda, thank you once again for your reply.
I do consume a fair amount of fish, this is true, however I believe salmon is one of the safer species in terms of mercury levels.
I like the look of a Paragone, and the user testimonials appear to be positive. I tried purchasing from Amazon US and UK, but neither will ship to Japan (I haven't been able to find the product on any Japanese sites either). I may need to have it sent to a family member, then ask them to ship it to me directly.
Complete Digestive Stool Analysis is one of the tests I wish to pursue, but again, it's difficult to find a laboratory which performs this analysis for the general public.