The Text Shape Generator provided by TinkerCAD specifies that "They've shared the code, too!" When I view the code, there are instructions for adding extra fonts to the tool. The instructions are as follows:
Customize the fonts that are available by following these directions:
1) Find an SVG font to use, http://www.fontsquirrel.com has some for example
2) Click on 'Resources' in Creative Library Editor and upload the font *.svg
3) Modify the 'fontResources' variable below to include the new font.
The object is defined in the format: "Display Name" : "Resource Name"