The TK-2312 was discontinued a while back and replaced by the NX-1200AVK.
You might find some dealers with TK-2312 still on the shelves, but you'd need to start calling them and asking.
If you cannot find any, the NX-1200AVK is the analog only version of the NX-1200 List price is about $290, but you should be able to get them less than list.
You'd need new programming software (KPG-D6NK), as I'm sure you've guessed, and that's going to set you back $104 list price. Your programming cable from the 2312's will work, though.