Customization is done differently in India than it is here - there are many small shops that will do far more than just bolt on parts from a catalog. You can get pretty much any custom mod that you can think done up in places like Mandi Dabwali, where there's a vehicle customization "market" made up of many small shops like this:
I wrote earlier that there's a similar area on the outskirts of town with many small shops that do custom truck bodies for Mahindra PikUps. Speciality fab shops like these exist all around the country and often when one is established, more will spring up in the same area doing similar work. This is true in India for many products, for example where teak and other woods are present, a "market" of furniture building "factories" is likely to exist. The word factory is also used a bit more loosely in India, a factory could be a small garage or even a single room in the case of fabric products.
Also in India there are a number of replacement body part manufacturers. You can get everything from a single replacement panel to a complete Savari body. For example:
Building a pickup? How about a complete bed? Nice diamond plate interior...
The manufacturer of the parts above is here: