I’ve no clue about emulsion making and sensitizing. However I found this webpage with a catalogue of dyes:

http://www.organica.de/en/produkte/f...le-farbstoffe/

Perhaps it helps you. Some are marked as sensitizer in the specifications:

For example CAS 52749-17-4 is maked as „Red sensitizer in photography“:
http://www.organica.de/img/products/...cification.pdf
which is quite affordable at Sigma:
http://www.sigmaaldrich.com/catalog/...ldrich/t159859

Chris