You might be in the wrong hobby if ...you want a sewn-in floor in a period-type A tent.
That said, so many reenactors have tents with "mud flaps" sewn into them. These are about 10 inch wide sewn-in flaps that lay on the ground along the long sides of the tent (and attached to the back entrance flaps at the bottom). When deployed, they lay on the inside of the tent, covering that otherwise open gap all around. When combined with a separate canvas ground cloth to lay over them, it's practically the same as having a sewn-in floor, but with the advantage of keeping the (wetter, dirtier) ground cloth separately packed for travel and replacement.
This may be what your wife has seen at reenactments. You can order a tent with these optional mud flaps sewn-in (just ask, or see sutlers at camp or online), or go to any canvas or tarp maker or repairer and they will quote you to add mud flaps if you can describe them. Might be about $100 in the Midwest. If you're handy and have access to a heavy-duty sewing apparatus (some are manual) I've seen them added by amateurs.
Here's the thing; though not so much a military standard at the time, there was no preventing any officer or officer's wife from having a tent modified to their own specification, which is kind of a "justification" for reenactors to have mud flaps. A particular supply depot might have even supplied them that way standard, we are to suppose.