You can simply go to the GTN and type "augmentation" into the search field; you will need to tab way over towards the last few pages before you will begin to see MK6 augmentation kits. The MK6 kits will usually cost you anywhere from 30K to 40K credits on the GTN - PLUS - the cost to actually install the MK6 slot on your equipment is right at 30K credits per slot (adding a slot will also consume the kit)
You will spend a ton of credits going from MK1-2-3-4-5-6
If you wait until your character is able to utilize the MK6 Augmentations, install the slots one time and save money
Not to sound really slow, but where is this magical GTN I keep hearing about? I have a lvl 25 sith assn and have yet to see a npc/store that will help me use the mk# slots I've collected or let me search for anything.
Other than that, thanks for the info, I was wondering if I should bother since I get new equipment every few hours. Seems like I'll just wait and lvl for a while.