Which printer do you have? Do you want to use matt or gloss paper?
I found MIS to be a great source of all the little bits you need to mess around making up your own inks and filling cartridges. There is now the 'Ebony' ink which can be diluted to give all the shades you need, and that makes it very economical. I also used Epson ink from the large cartridges, but now I think I would start with the Ebony. It has also got good longevity ratings, and it is quite neutral on its own. There's more info on the Roark site. I made up my own inks mainly because I wanted a system for printing on gloss paper, and one didn't exist back then. I used (and still use) IJC/OPM for most of my systems, but now I would recommend QTR even though I prefer IJC/OPM. QTR is in much wider use.
It's an interesting project in itself.
Good luck,
Helen