A wood floor can be stripped and restrained, so your contractor will purchase a floor of the same kind and put it together with the old floor. Sand it all down and restain. You won't even know which is new and which is old. We do this a lot. Get a good floor guy.

Yes that floor can be purchased unfinished so you can sand entire floor and stain and finish.

Red Oak narrow strip (probably 3" wide or so) that is solid hardwood looks to be your floor (with a stain of course). Pretty easy to come by. I'm not sure why you believe this is "impossible" to find. This is one of the easiest in N. America to source.

It sounds like you are looking for a way to leave this hardwood alone (no sanding, no refinishing, no staining, no "extra cost") while installing another floor. If that is your wish, then go ahead and remove the wall, and install a floor that you think looks good.

It will require some sort of decorative trim that outlines the new area in a pattern. This will effectively create a defining area of one space to another....kind of like a permanent area rug that you can never get rid of. This is the "cheap" way.

If you do it the "cheap way" (leave the old hardwood alone), then do yourself a favour and MATCH the wood species and the cut. This means you can sand and refinish both floors later in life and have them MATCHING.

You will always live with the decorative trim that will follow the old wall line...but the species will be the same. In the FUTURE you can have the floors sanded and refinished without worrying about getting two different species to take stain...which is difficult to do and can have HORRIFIC results when the "floor guy" is poorly trained/cheap to hire.

Good luck. We've given you the "correct" way to do with and the "cheap way". The choice is yours. Have fun.