Once you're received the tap and done any necessary cleanup/renovation work on it to be serviceable you prepare your dowel1, thread a portion of it, then determine what the pitch and profile is. Once you know this you see if you can find a matching tap for sale somewhere.
Given the typical thread profile for modern wood taps and dies (90° V-threads, ...
You have two choices:
Find and buy the parts you need.
Design the part you need, or have someone design it, and then machine it, or find a machinist to make it.
Details related to the "how to do this" question implied in (2) is out of scope for this SE.