This is another option:

http://www.ioffe.ru/SVA/NSM/nk/index.html

But I did not found your materials. Maybe this link will be useful in a future.

Also you have

http://www.semiconductors.co.uk/propiiiv5653.htm

Although the InAlP or InAsP ternary compounds are not listed, their dielectric constants (directly related with the refraction index) are close, so probably using Vegard's law you can interpolate a close value for the material you are looking for.

Hope I helped!

http://www.semiconductors.co.uk/propiiiv5653.htm

Sadao Adachi has published numerous papers discussing how to model the below-bandgap refractive index of quaternaries such as AlGaInP (Journal of Applied Physics, 75(1), 1994 pp. 478-480) and InGaAsP (Journal of Applied Physics, 66(12), 1989 pp.6030-6040). The ternary limits you seeks are included in above.

http://www.semiconductors.co.uk/propiiiv5653.htm

http://www.ioffe.ru/SVA/NSM/nk/index.html