Refer to the thread entitled "How to upgrade outlets and switches" wherein the OP seeks to replace some incorrectly-installed grounding receptacles with either non-grounding type or GFCI's. I also had a similar problem but with only one outlet. For some reason the ground, normally supplied by the AC cable, was missing even though a grounding duplex outlet had been installed. IOW using the standard neon light tester I could not get a circuit between hot (black) and ground on the outlet, nor between hot and the metal box. I suspect that the cable was not properly clamped to the box there or at the previous box but since this is an infrequently used outlet I wasn't planning to pull the cable to investigate. All other boxes on the same circuit had ground. The box was far too shallow to install a GFCI so I decided to put in a non-grounding duplex outlet. Then the problems began.
Naturally I checked the most competent suppliers (Lowes and HD) first. Lowes had non-grounding duplex receptacles in ivory and white and HD had them only in white. I really wanted brown to conform to all the other switches and outlets in the house so, thinking of how much better the "real" electrical suppliers are according to the "professionals" on this group, I set out to find what I needed.
First I tried the "real" hardware store where everyone is treated as a shoplifter. You not only can't browse because such an activity would take up the expensive conditioned air of the store but everything that could be physically lifted is kept under lock and key. The owner, taking time out from complaining about the government with his layabout cronies deigned to acknowledge my presence with "Yeah?" typical of such establishments. I ask for a non-grounding duplex receptacle in brown. He grunts and disappears into the back. Several hours later--it seemed like that but was probably only ten or so minutes -- he reappeared and tossed a grounding receptacle on the counter.
"Er no," say I, "That's a grounding receptacle. The non-grounding type has only two pins." Mind you, give him his due: He did get the color right.
"That's all I have," says he, returning to his debate about how the liberals are ruining the country.
OK, let's move on. My son happens to work for a large commercial electrician; the type that wires up large buildings and factories. He's always offering to help me with any electrical problem and he is on a first name basis with the counter jockeys at (supposedly) the largest electrical wholesaler in the region. So I explain what I want and even give him the ivory version I purchased from Lowes.
According to him his encounter with the electrical supplier was far more cordial than mine was with the hardware guy but still resulted in a look of amazement at the receptacle and a statement that they couldn't sell him one because "it's illegal". Although he pointed out that it's for him personally and not to install on any commercial job they were adamant.
He continued looking at some of his hardware contacts and in the meantime I checked that a brown one actually exists. It does. Leviton list it as part #223.
So off I go to my more residential-related electrical supplier and after patiently waiting my turn behind half-a-dozen electricians all discussing how the liberals have ruined the country, the counter jockey finally gave me the standard, "Yeah?" I proceeded to explain what I wanted and his reaction was, "You need a time machine."
Much merriment among the electricians at this witticism. I then point out that it's currently made and is shown in Leviton's catalog as part #223. Amazingly they had actually heard of Leviton (I'm being sarcastic). However their reaction was to tell me that I didn't need the non-grounding type because any receptacle would be automatically grounded when I screwed it into the box. The "professional" electricians nod gravely, thinking no doubt that this is a particularly stupid home-moaner. In most instances they're correct because all the wiring in the area is and has been since the dawn of time either conduit, EMT, or AC. However at no time did they suggest that I test that a ground was actually available at the box. Very dangerous advice.
I gave up and installed the ivory receptacle from Lowes.