There are detailed instructions for making your own bullwhip on EM Brand Whips home page. Thanks Bernie.
Here’s a PDF I wrote Make-A-Snake in which I show how you can make a simple snake whip out of nylon braid from the hardware store. It uses only the most basic braiding and takes less than an hour to make, but will do a forward crack quite nicely.
The 1892 book Picturesque Hampden has a section on a whip manufacturer in Westfield, MA, which was the center of the 19th Century US whip industry. Start here and press Next button to read the article. There is one surviving whip company in Westfield using 19th Century whip making equipment.