I don't think you should be concerned about JIS or ISO taper because you're most likely not going to find another crank that can use a 124mm spindle! Are you sure that's right? Choose your crank a get a new cartridge bottom bracket in the size that crank calls for.

If you wanted to gear it down a bit, the Sugino XD is a very nice crank for a good price. You can look at them at rivbike.com and probably find them cheaper elsewhere.