There used to be a producer for track with concrete ties in Germany - discontinued due to lack of demand.
Apart from that, just like I suspected, concrete ties with Pandrol rail fastening hardware won’t be sturdy enough if done in plastic (the hardware!) and too expensive if done in metal.
BTW as far as production is concerned that shouldn’t be a problem, you finance the development of the injection mould, request a large enough order of tie strips and they will do it for you.
You could also design tie strips to be 3D-printed as test pieces to find out just how much structural stability - in model railroading aka as oversize - it will take in plastic
As far as the proto, up here in the Great White North, is concerned, the jury is still out on the concrete ties. Based on what has been in use i.e. what used to be produced in the past was not the cat’s meow. There was an article in TRAINS on the subject.
AND well shaped, properly maintained track with plenty of fresh ballast, heavy duty rail and heavy wood ties looks just as good as concrete. Of course that’s just my opinion.