Are there any suppliers which sell fluorescent dyes, such as fluorescein, rhodamine, oregon green etc in large bulk volume, such as 1-2Litre bottles?

 

Many thanks in advance.

Uh. Litres? No idea. But as they are more stable in dried form I would search for that instead. Sigma for instance sells 500 g of rhodamine for around 130 bucks, fluorescein was around 200, I think.

Look into supply companies for ecology and watershed management. Non-toxic colored dyes are often used to evaluate stream flow rates and watersheds.