Alright history relics are one of the many different types of collectibles that be found in Mad Max. There are a total of 103 of them. They're most similar to scrap and can be found in Strongholds, outposts, looting locations, and vantage points. They look like little blue books.
You should get most of these while going for the
achievements so you shouldn't focus on this until after completing those. It is worth noting that sometimes these will glitch out and become invisible and if that happens you just have to hold
where the collectible should be.
If after completing the game you still haven't gotten this achievement press start>collectibles>history relics. Look for any that show a question mark and then figure out what number it is by counting off from the bottom going left to right. You can use this detailed IGN guide to find the exact ones you're missing http://www.ign.com/wikis/mad-max/History_Relics#Relic_101