Hi Danijel! Sorry for the late reply. It’s certainly possible to buy a bike from another long-distance tourist, but that will probably entail A) lots of time on local sell/trade websites(try OLX and yapo.cl), B) asking around at bike shops, and C) luck. A lot of bike shops in Chile/Argentina are informal workshops that someone is running out of their house, but you can find them by asking around: “Conoces a un taller de bici?” I wouldn’t expect to find anything in Villa O’Higgins. It is very small and incredibly remote, and most who pass through there will continue south into Argentina (via the Lago O’Higgins ferry) or north into Aysen along Ruta 7. Your best bet for buying a bike somewhere south of O’Higgins would be El Chalten (just across the border), El Calafate (the regional capital and the only major airport for hundreds of kilometers — just three or four days’ ride from the crossing into Chile and the beginning of the Carretera), or Punta Arenas (much bigger city, but much further south; not practical unless you’re planning on riding an extra week or two north through the pampas to reach the Carretera). If you’re willing to ride north-to-south, you might try looking for bicycle sellers in Coyhaique, the regional capital of Aysen, which also has an airport. If you’re starting from home, don’t write off the possibility of buying a bike at home and taking it on the airplane with you. Many airlines will carry bikes (when properly boxed) for fees of $100USD or less — and Sky Airlines, a Chilean domestic carrier, will carry your bicycle for free.
Feel free to reach out with any other questions. Good luck, man!