The word "aftermarket" refers to products or parts that are not made by the original manufacturer of something, like a car. These products are made by other companies and sold separately. Full definition
They add additional accessories, replace parts with aftermarket alternatives and treat their bikes as a hobby. (consumeraffairs.com)
It's a configuration many enthusiasts will no doubt prefer, due to its familiarity and the widespread availability of aftermarket upgrades. (motoring.com.au)
The department's mission is to provide the automotive aftermarket with outstanding professional development and training resources. (sema.org)