It depends. Lots of parts are shared by multiple models or even companies so it may be the case that nobody has made for example a new water pump specifically for your car for 10 years, but the design is the same as the 2025 something else so you can just use that one. There are also warehouses with older parts that can last for years. You can also pull replacements from junked cars that have not been crushed yet. In some cases third parties manufacture replacement parts when the supply runs out, but those replacements are often of poor quality and sometimes are only vaguely shaped correctly and require extra work to actually fit on your vehicle. Keeping old cars running is a challenge, especially if the car was obscure when it was new.