I've got a couple of thousand of these in the house. it's a shame I can't send the to you through cyberspace. Anyhow, I'll try to explain a little about these before telling you where to source them.
Originally these tablets were known as Glycerin and Thymol tablets in the old pharmacopoeia used by doctors, dentists abd pharmacists years ago. It was possible to buy a concentrated version in the form of a liquid for dilution with water. However, these tablets became gradually unpopular as more powerful oral antiseptics were developed, as Thymol itself is a fairly weak antiseptic.
Normally, these tablets are only available from specialist dental suppliers who are only interested in customers who have accounts and spend a good few hundred pounds per month withe them.
However, a contact in my university dental school suggested you get in touch with these people who can sell you a single tub of 1000 tablets at a reasonable price:
http://www.brosch-den.co.uk/acatalog/Mouthwash .html
The active ingredients are the same in all the colour varieties, so if you fancy an alternative to pink, you have four others to choose from.