Hi Bertil,
Full size rails are roll-formed white hot with a set of two powered rolls. There are usually several "stations" along these rolls to progressively form the rail profile. The bar moves through the rolls then is moved back through the next station, etc.
It could be done for model rail but would involve making the hard steel rolls and a sturdy frame to hold them, and finding a motor gearbox system to drive them. Probably 750 W or more of output power would be needed for driving the rolls, depending on size and heat of the rail. An induction heating coil setup could be used to heat the rail to white heat quickly and continuously as it is fed to the rolls. There are specialist suppliers of induction heating equipment for industry and for blacksmiths an knifemakers who could probably supply a suitable heater unit. Water cooling of the rolls (could just be a water hose sprinkler system over the rolls) would be needed to hold their hardness.
Some experimentation on the roll profiles and heating parameters will likely be needed as well as testing of the finished product to make sure it does not have cracks or other defects. There are some youtube videos of full size rail rolling to give you a general idea of the roll shapes and number of passes needed.
It's a rather big undertaking, but once set up, you could make a large quantity quickly a couple of times a year and maybe sell it to other clubs or hobbyists. Note that the profile of some British rails is a "bullhead" style that sits in cast chairs – this is quite different than the flat bottomed rails and tie-plates as used in North America and other countries around the world. JD