Quick way is to activate the editor and use the option it has, press f1 listen for the activated then activate unlimited resources when you are in the base so you can access the market, and you need to go under the market place and sell 1 of each item you want to max out, and it should change the amount to 999999, just make sure to have it activated.
If you are in doubt about it being on or not sell 1 of the sectoid corpses since those are easy to come by, and once you have the specific items you want turn it off make sure to save afterwards it has crashed a few times for me after i used the resource option.
I'm using the editor and it doesn't seem to work for this. Just got the game from the Steam summer sale, and when I go in to the gray market and sell an item nothing happens. Does the editor still work?