Might check through your State extension service or land grant university. Many of them offer the service (primarily for rural residents w/ their own wells or for monitoring for ag runoff or livestock operations, but at least here they'll test any sample of a State resident).
Unfortunately, probably what you're trying to test for isn't the ordinary coliform or similar so may not be quite so straightforward as one would hope to show what the "problem" is that the utility needs to fix. If it meets the safety standards of no biological hazard, "appearance" issues aren't nearly so tightly regulated. IOW, it may well be within all the applicable regulations but still not particularly palatable, unfortunately.
Guess you could always go open the hydrant yourself on occasion... :)