You can get the grommets from any hardware store - Lowe's, H Depot, etc.
For the tubing, are you talking about polyester expandable mesh sleeving? Looks like this:
If so, go here: http://www.mcmaster.com/
then in the search box type "mesh sleeving," that's what I use for my tower and running the wire - just make sure you get the right size for the amount of wire you're using.