I have a reprint of a 1902 sears catalog. It only has one 8 gauge listed. It looks like they only offered a single shot break open at that time. I think it was such a niche weapon, for market duck hunting, that the average man wasn't likely to want one. They only offered a relatively inexpensive single shot for the odd person who desired one, and didn't put too much overhead into stocking a wide selection. Even the 10 gauge wasn't too terribly popular then, back when lead shot was legal.
As an aside, I can remember an article in some NRA magazine about a british guy who made a two gauge single shot goose gun. In england the gauge restrictions weren't as stringent as here, so the waterfowl got wary and english gunners went to eight and four bore guns to reach out and touch them farther off. The two gauge fired something like a 16 ounce proof load! I wouldn't want to shoot it!