Hi Chris,
Unfortunately, I have no ideality factor and series resistance information for the LM99. I was unable to find the information from the previous Apps Engineer. Most of our portfolio is all fix ideality factor and series resistance; however, LM86 might work for you, but there is an offset that you need to take care. Do you know what your temperature range is?
I would suggest you to look into TMPxxx devices (TMP421, TMP422, or TMP423). The beauty of these parts is you can program the non-ideality factor correction and series resistance cancellation; however, I do not know the guarantee specs.
Aaron
