Even so, I'd be looking for the smallest sprouts you can find. They grow down pretty quick looking for water.
At my place, you can find the oaks when they're about 6" tall and have a cluster of leaves on top (the ones the deer don't nip off). If you dig down about a foot the tap is starting to get fine enough to where I'd imagine breaking it off there wouldn't be a big stress on the tree if it was watered in well at transplant. I'm not sure a potted seed grown oak would have any better odds (the pots aren't deep enough). I've found those tend to have j-rooted taps and that's probably harder to overcome than acute root damage.