The usual suspects sell them - eBay or online store. This would be your last option though. Unless the originals are rusted, you should be able to follow Marty's advice, or use Ranex as I have successfully done on tons of chrome legs.
If the legs are for your Flash - you might be out of luck - The 28 1/2 Chrome legs sold locally are ribbed and used on WPC games. The original legs can be sourced from Pinball Resource in the US.