Apparently there is a Lenovo miix 2 tablet with this capability. Seems like there should be other choices out there, but after talking to the apple folks there is nothing in their product line that has this capability other than using wi fi which is useless off shore. I've been using a garmin product for over 5 years now that fits on my wrist that tells me my speed while I jog that has the built in gps antenna. You would think that tablets could have this capability without having to get a service contract with the phone company.
I have both Miix2 8" model and iPad.
Regarding the Miix2 8", yes it does have GPS built in, and it works without any WiFi, though initial fix can take a few minutes if you're booting up a mile or so from where you last shut down. With WiFi it seems to get a faster initial fix, presumably because it has a good guess of your location from WiFi mapping. But it definitely works without WiFi (or 3G/4G).
Note that only the 8" models of the Miix2 have built-in GPS. The 10" and 11" models reportedly do not have GPS.
Also note that Microsoft's support for tablet GPS chips is a little odd under Windows 8. Out of the box, the GPS only works with Metro apps. Windows programs that are used to seeing GPS on a COM port or TCP port will not work. But there are free and low-cost utilities that will create a COM or TCP stream from the GPS, so that fixed everything.
I am shocked that any Apple Store employee would give you such incorrect advice. Apple tries to be better than that. If, on the other hand, "the apple folks" are Apple enthusiasts on Internet message boards, then you get what you pay for (or less). As Stumble said, buying an iPad with wireless 3G/4G capability gives you a fully functional GPS. It works perfectly fine when you're out of radio range (I've confirmed this with our own iPad). And if you don't want to pay for the wireless service, just don't buy it.
FWIW, I run OpenCPN under Windows 8.1 on the Miix2. I still like it better than any iOS or Android app I've tried. YMMV.