Digi-Key sells everything, and will let you buy in onesies and twosies without screwing you on the price. Maybe Monoprice for cables, but that's rare.
The one time I needed a DB-9 gender changer in a hurry and paid freaking $20 for it was the day I decided I was done with RadioShack. You served a great purpose, dear friend, but times have changed. I still have my Pocket PC-1 for the memories.