My last article discussed how I store my jewelry. I mention the plastic bag and anti-tarnish strip method and provide a link to Fire Mountain Gems - a seller of anti-tarnish strips.
However, you can just do a google search for '3M anti-tarnish' and find many different vendors of anti-tarnish strips and tabs. You can find small jewelry size plastic bags at Wal-Mart, JoAnn Fabrics and most craft stores like Pearl'sand Micheal's. I've also purchased them online but there are large minimum orders.
Worried about the anti-tarnish strip brushing up against your jewelry in the bag? Don't be - the active ingredients in the strips that retard the tarnishing do absolutely no harm to your jewelry.
As I mention in the article you still need to occasionally polish your sterling silver jewelry but using the anti-tarnish strips dramatically decreases the frequency.