I'm afraid I can't recommend any other labs (I do all my testing myself) but I know you can find them in the phone book, in the Grainger catalog (you buy a kit of empty bottles, fill them up and Fedex them off - the testing is prepaid when you buy the thing) etc. The problem is that none of them, that I've ever seen, gives you the set of stuff that Ward Labs does at the price. I think they did screw up on your RO sample but at the price they provide and awfully good service for brewers, IMO.
The problem with shipping is that the sample can lose CO2. This happens with more with samples with at low pH since much of their carbo is in the form of dissolved CO2. This can throw an acidity measurement way off but brewers aren't really interested in acidity, just alkalinity and alkalinity is little effected. Just as an example a sample with 6 mmol/L carbo at pH 6, where 70% would be carbonic, has an alkalinity of 88 ppm as CaCO3. This is not that unreasonable a pH for some wells, by the way. If such a sample stands to the point where the pH rises to 7 it will have lost 3.82 mmol/L as CO2 gas but it's alkalinity will be 89.5. That's not much of a change so you only need worry about shipping WRT alkalinity if you want the most precise analysis and there is really little need for that in home brewing.
The other problem with overnight shipping, and I think this was mentioned earlier, is that microbiological testing results can be skewed if the sample is not processed within 12 - 24 hours and is not kept cold between collection and testing.