Wedges of the kind you describe are fairly easily available at my local suppliers. I believe one like the round thing you describe has been advertised as "The Exploder," which sounds a bit overblown for the performance I'd expect, although there are lots of testicalmonies for it in the ads.
If nothing else, try a current issue of MEN1 and search the ads.
An ax is of course the "macho machine" but generally a good wedge and maul is more efficient for splitting, and a saw is more effective for cutting - usually - depending on circumstances - and on the weather - and on the health and philosphies of the user. A "splitter axe" is something of a compromise.
1 MEN = Mother Earth News, although there are lots of "minimalist" and "survivalist" magazines with somewhat similar content - at least for the advertising.