Best places to get parts and accessories for a project?

I’m slowly researching and gathering parts for my bike and getting ready for spring to roll around. This is the first time I’ve done real work to the bike so I’m curious if there’s anywhere in particular you guys who have more experience would recommend getting a new set of handlebars (and/or good brands) from and where is the best place to look for a nice seat (since I don’t want to cut mine apart and make a new one)? Something like revzilla? Amazon? Individual companies? Brick and mortar stores? Thanks in advance via /r/CafeRacers https://www.reddit.com/r/CafeRacers/comments/eugwug/best_places_to_get_parts_and_accessories_for_a/?utm_source=ifttt