snap ring pliers with a 90 degree bend work well, as long as you get a quality pair. The cheap ones don't like to work. I have used two 90 degree picks with success, and I have used 14 gauge solid core wire successfully... just route it through the holes and yank.
As far as new retainers go, get ahold of Larry Granback at Motor Pro sales, in Midlothian, VA. Their number is 800-468-5700 and you want part number C468 - it's a box of 25 of them for $20.63. They have a website but you still have to call to order. Shipping is very reasonable and you'll get them within 3 days. I think mine were about $25 shipped. And, you'll have enough clips to replace them all 4 times and still have a spare left over. Actually, it's getting about time for me to order another box myself...