Your model is significantly newer than many of us here who are also devoted to the TWI stuff.
However, the age of the sensors is a problem, and none being made, plus most stations seem to be taken down by survivors after the house is to be sold, and they are abandoned, with many more stations than sensors.
On the older models there are known replacement sensors (board level) for the temperature diode, and one or two reports of the correct Honeywell humidity device, with if I recall correctly one user saying he has replaced his at least a couple times.
Some day we may have a board layout or a point to point wiring diagram (I'm partially to blame for not doing it with all the other things on my plate) to try to make your own. Whether TWI used the same circuitry in the one you have is unknown.
Send pictures of the item you need to replace.
PS, I look on eBay every now and then with zero success for sensors. A few display-less boxes, but no sensors.
Dale