Tons of people want old west style guns. Part of the reason it is viable for companies to make modern repros of 1880s and earlier guns is simply due to the fact the quantity of those firearms produced were relatively low (limitations of technology etc.) and the condition the originals tend to be in is fairly poor. Coupled with the fact that since the condition is crap and the price is high very few people can reasonably afford to shoot a original.
A C96 Mauser was a very expensive firearm to produce, now it would be even worse. A better option might be that Spanish 'copy' which was simplified as it is very similar (I believe it had the name Astra 700 or something of that nature) appearance wise but would be easier to make. In regards to the Webley in .38 special, your really starting to push the limits of that design with that caliber. Generally speaking most people are more interested in swing out cylinders, and generally prefer it to be .357 so they can choose between .38 or .357.
Another thing I just remembered there are companies making M1Carbine repros and such and they tend not to sell to well as most people are willing to buy a original rather than take a repro.