If you are not after low concentrations of rhodamine, just get a
bandpass filter, like Edmund's #A43,076 (diam. 11.8 mm) or #A43,128
(diam. 24.15 mm) and glue it in front of your eyepiece.  Depending on
the diameter of your microscope's focusing tube, choose the proper
diameter and vignetting if necessary.

Edmund Scientific is @ http://www.edsci.com.

Good luck.

Alex