Foot caps and ladder treads are generally not available as replacement parts through the manufacturer, as these are considered a normal wear and tear item. A variety of third party options available online or at your local hardware stores, however.
There are a few exceptions to this rule, and we are always happy to look at available parts for your specific model. One example is the Stylaire Retro Chair, model 11120. It made its debut in the 1950's and was reintroduced in 2010; although some improvements have been made to the overall design of these chairs, foot caps and step treads are available for purchase and will fit either versions.