Hello Janet P! Have you tried to find your alternative to new Gamboge yet? You didn't mention which medium you were looking for, but as there will be differences between Oil / Water / Acrylic, etc, then this will have a bearing on the outcome.
If you're using watercolour, then you could try Aurelin, which may be about right, but failing that, one of the Cadmiums (Acrylic or Oil) should give you somewhere around the required shade.
I've used Cadmium Yellow Deep and been quite impressed by its tonal range, from quite red (strong) to mid (weak).
You didn't say why you wanted an alternative; I'll be interested to hear why.
I hope you do find an alternative!