Partsmovers normally have the right part that you need. Some can be more expensive than others. AutoHaus for example specializes in selling Mercedes Benz OEM parts.
Euro Parts produces decent replacement parts for a low price point. So, they are an excellent option if you are trying to maintain a car on a budget.
However, be aware they don’t put a country of origin on their products. Buying an aftermarket blower fan can be a great option because it costs less. But, save money for more important parts that can impact the engine or other moving parts.
Phoebe Parts is another company that makes decent replacement parts. Their parts are all made in China, but their pricing is generally much lower than buying from Mercedes or other places.
There are a number of other trustworthy brands that you can rely on to get parts that have good quality control. The main thing to look at would be the country of origin. For example, parts made in US will have a higher standard than parts made in China, Vietnam, or Taiwan.