If your case didn't come with any, any thing Velcro strips could work (search for Velcro ties). I usually just use plastic zip ties - they're cheap and thin, and can often anchor to narrower points than Velcro strips. Long ago, I picked up a big bag from a hardware store or Newegg. It's since run out, but most PSUs, cases, and motherboards come with a few, so my supply is still okay after all these years.
The biggest thing for cable management is routing: try to find the shortest, logical routes, and try to hide the longer parts of the cable runs behind the motherboard. Use the case cutouts.