I used to use InkTec for HP, and it was good. I suggest also that you contact WebSnail on this forum (I forget his company name), or Precision Colors in Canada. They will have what you need.
I bought my inks 2 years ago for my MG7150 (same inks I think for the MG7550) directly from Aomya in China,
the dye inks were 3.80 USD per liter, and the pigment inks were 17.80 USD per liter !