You can apply cold bluing yourself but it won't look as nice a dipped hot bluing or be as durable, especially on brake disc for a bike. Any gun shop should sell small bottles of Birchwood Casey cold bluing and I think wally world carries it too. You'll need some type of degreaser such as brake cleaner, the bluing, rubber gloves, 0000 steel wool, cotton swabs and a clean cotton rag.
It might be a fun and cheap project but you get what you pay for. I myself wouldn't have them blued at all because of the rust issue but that's just me. If you're still interested PM me and I'll describe the process I use.