Is "red dye #3" the same as erythrosine?
Yes. From wikipedia: "Erythrosine, also known as Red No. 3"

Try Alfa Aesar. Erythrosin B is listed on their website. They will only ship to a business address but they were going to sell me a small quantity of Eosin Y for a reasonable price. They also list a number of other dyes, including cyanines.

-- Jason