Red and Green dyes are available through Sands. The price is about $100 / gram or more.
Blue sensitizers can be had from Honeywell in Germany for about the same price.
AFAIK, neither list them on their web sites, but you can e-mail them or call and they will give you product numbers.
But, don't use a blue filter. Since a plain raw emulsion is blue sensitive, no filter will give you much higher speed.
Best of luck.