There were two Wheelers that fit the time period; one with no first name in London 1804 - 1808 and Robert in Birmingham from 1798- 1813. There was also a George Wheeler in Virginia in the early 1800s. There were a number of other Wheelers but they were too late for your gun and lock.
The gun is almost certainly made in the US but I feel the lock is almost certainly made in Britain and I am suspicious that it may have been salvaged from another gun before being used in the present one. I am assuming the lock fits the recess closely. The lock is a high quality lock and seems too almost too fancy to have been purchased originally for the gun (as opposed to being salvaged from a damaged gun) I also get the impression that your gun was once a full stock and most of the forestock has been lost.
You might find the name of the american maker on the top of the barrel. If you remove the barrel, conceivably you might find a (barrel) makers name on the bottom near the breach and possibly proof marks.
cheers mooncoon