The "Replacement Parts Availability Act" amends the Toxic Substances Control Act (TSCA) to mandate the exemption of replacement parts for complex durable and consumer goods designed before a relevant rule's publication, ensuring their continued availability. The Environmental Protection Agency Administrator may only regulate these parts if a risk evaluation finds they significantly contribute to risk for the general population or a susceptible subpopulation, requiring an express written determination supported by substantial evidence. The bill also prohibits the Administrator from restricting the manufacture, processing, or import of chemical substances necessary for these exempted replacement parts, provided their use is limited exclusively to replacement part manufacturing. Furthermore, if any prohibition or restriction on replacement parts is permitted, it must include a transition period of not less than 10 years . This legislation aims to balance chemical safety with the practical need for maintaining and repairing existing complex goods.