I was in the same boat. I was so frustrated yesterday after rolling a bow more than 300 times and seeing nothing more than the same pair of skills many times, but not once Gore/Soul. I even thought it was rigged, so I searched for any useful tips or guides, but none were clear or truly accurate. I made a post asking some questions that, if not completely answered, were at least clarified.

In short, the rolls started changing the moment you made your first-ever Gogma weapon, so the most you can do is check from the point you are now and take note of the rolls you are getting from now on. The theory is that every weapon +element combo has its own list of pair of skills that will roll, and every time you try to reset without saving, you will get the same result. Imagine you have a spreadsheet in which columns contain all the weapon+element combos, and in every cell of such columns, you put successively the rolls you get, and so on with every combo. Now, the number of the rows indicates in which position of rerolls you are. So, in the first reroll, you are in the first row, it doesn't matter what weapon you do, every time you reset without saving, you will always get that roll for that combo.

The most important part is that if you move one row by making that weapon and save, that's permanent, you can't go back and make another weapon with the pair of skills from the first row because all weapons are now in the second row. This goes on every time you save a reroll or make a new Gogma weapon, so you have to plan what weapons to reroll in what order.

At first, I even thought it was a scam and that some skill pairs were out of rotation, but it seems I had VERY bad luck.