The first step is to have access to a 3D printer. Although it might seem intimidating you will quickly learn that 3D printers are easier to use than ever. The most difficult part is setting it up to ensure you have a good print. Usually libraries or schools will have someone who has experience with these machines. There are also very affordable consumer machines out there. The machine I built back in 2004 was a Makerfarm Prusa i3. Later on I used my sister's PrintrBot Simple Metal, as shown in the images below.
The second step is to start printing! You can download the files for free in the download page. Make sure to print with 100% infill. When printing I recommend printing a brim to keep the yoyo lifting from the print bed, which would cause the yoyo to vibrate. Don't feel like purchasing a kit yet? Perhaps try printing a test half first. If the results are good, pick up the Fluid Print Spacer KIt in the Products page. Another benefit is you can purchase one set of spacers, and have 2 or 3 different sets of halves you can play with. Feeling adventurous? Try designing your own yoyo!
Of course the final step is to assemble the yoyo. The kit includes the custom spacers, an axle and the two nyloc nuts. You will need to source some 19mm response pads and a C-sized bearing - but you can also take those out of your existing yoyo. Assembly is very straight forward. See if it works out and adjust the print as necessary!