Ugh, G3 charms and brushes :S What I did when I was trying to match them, I would google a pony I have, start out with Mylittlewiki, or just google MIB pics, and then see what she came from and match it. It worked pretty well, but I had under 20 G3s I had bought MIB back in the day that I had to go through.
I can say I know that Sparkleworks came with an orange charm ^^ but I don't know if she was the only one.
EDIT: also, according to this pic
http://mylittlewiki.org/wiki/File:2003-minty-promo.jpg The green one you have might have come with Minty.
I have noticed that most charms match the pony colour, so I would start by searching through ponies that are the same colour as your charms