Hi Avril,

I recently did a fair amount of online research on royal (Tyrian) purple
dye, while preparing an article for American Conchologist.  I did not come
across any place that offers the dye itself for sale.  This is no great
surprise, given the difficulty of producing it, and the consequent high
price, compared to comparable modern synthetic dyes which are far easier to
manufacture and much cheaper. However, I did come across a little book that
supposedly gives recipes for preparation of the dye.  Perhaps your inquirer
would find it interesting. It's called Tyrian or Imperial Purple Dye, and
can be found here, if anyone is interested:

http://www.georgeweil.co.uk/pdf/21_natural_dyeing_books.pdf

He/she might also find this interesting - a bibliography to literature on
Tyrian Purple:

http://www.chriscooksey.demon.co.uk/tyrian/cjcbiblio.html

Regards,
Paul M.