There are in fact, a finite number of artefacts in the game. These are split into two categories:
Wild artefacts - There are only ten of these in game. You can only use them on gates that don't need a specific artefact. If you are stuck finding these, there's a handy guide here
Regular artefacts - Each of these correspond to a specific gate and are generally to do with story progression. As you'd expect there is one for each gate. Likewise, you can find a guide to finding these here. I wouldn't recommend using this guide though, whereas the wild artefacts can be difficult to find, these are part of the natural story progression and not that difficult to obtain. They're generally awarded as a sort of 'Level Complete' reward
On another note, it is strange that your brother of a friend should restart the game. You can complete the game without locating all of the Wild Artefacts. You will only need them all to collect all 160 fragments, and they don't need to be collected and/or open gates in a specific order.