Unless you are passionate about finding 100 year old plans and fabricating one out of steel using a lathe, a Bridgeport, shapers and all the associated machinery, its probably better/cheaper to find one at an engine show after doing some research. They aren't all that complicated but the folks who built them, sold them, serviced them and originally used them are most likely all dead. Of course there are collectors and the internet. You know, you can't just buy ONE.
You need 6 or 7 to make a good running ONE. Good luck.