I'd be very wary of shot blasting rims. If someone doesn't know what they are doing, they will be destroyed and anyway, they will probably need to be re-chromed afterwards.
If it's just surface rust, Brasso or Duraglitz will do the trick, otherwise try a kitchen scouring pad or fine wire wool soaked in 3 in 1 oil, then brasso. Don't use anything too abrasive or you will ruin whatever chrome you have left.
If this is for an everyday bike, strongly consider an alloy wheel, at least for the front. It's safer in the rain.