Where would I go to get the absorption spectra for common psychoactives? It seems like this would be a useful alternative to bioassaying when there's a chance of the product being toxic.

There are specialized books containing thousands of spectra. They are usually organized per class of compounds, for instance barbituratures, benzodiazepines, etc.

Aside that, there is also the scientific journal. My guess is you have to look for toxicological literature from the 70s-80s. UV spectrophotometry was much more common as confirmation tool in those days as it is today. Many labs didn't have these robust 5 m^3 MS in the days...  

A trip to the local university library will result.

I guess these volumes would be available for indices of refraction as well? How would one get the index of refraction for a compound (such as most of the compounds bees would be interested in) that was a solid at reasonable temperatures? Would these books include listings for such compounds in solution with something?

In some cases NIST or chemfinder will have the uv-absorbtion spectra curves for your item of interest. If you have the pure compound, you can establish a standard ( see my prior posts) and use that to determine you quantity of material in your sample

I don't know about psychoactives in particular, but here is a pretty large spectral database:

http://www.aist.go.jp/RIODB/SDBS/sdbs/owa/sdbs_sea.cre_frame_sea

That's a wonderful link! Much appreciated, the hive has come through again!