Depends on what you’re planning. If you’re looking to upgrade then there plenty of places like shopdap, BMP Tuning, uromotorsports to name a few. If you’re looking for OEM replacement of start with Rock Auto but the same sites I mentioned above will have all the OEM parts as well. Also, if you’re facebook, I suggest joining MK7 Golf GTI owners group. There are plenty of vendors on there eager to supply whatever you’re looking for.