I've looked on the internet including Amazon and eBay and can only find one person on eBay that sells them and his history is not great and I would like to have one by next weekend if possible. Does anyone know where else I can get one or one that is just as good?
You didn't specify analog or digital, so I went with the first one I found. The analog is just a calibrated thermometer that you use the wick in the water to get wet bulb readings. It works in any incubator.
Digital doesn't require any thinking to read, so I prefer them. But if buying a combined thermometer/hygrometer, be aware that they still need to be calibrated with known accurate ones before relying on them to sustain life.