Master Clue Scrolls - Although Master Clues can be the most difficult ones to complete but they're not so difficult to get. There are RS gold two ways to get them within the Old School version of RuneScape. The first is to complete simpler Clues. Master Clues are available from Reward Casket. On Easy Difficulty it's 1/5 chance, on Medium 1/30, on Elite 1/15 and Hard 1/15. The only Clue Scroll that does not have the one that is the Master Clue Scroll as a reward is for beginners.
Another method to acquire these scrolls is through a deal you can negotiate by negotiating with NPC Watson within Hosidius House. He will trade you his Master Clue Scroll for four other scrolls - Easy Medium, Hard, and Elite. This is a great method to eliminate scrolls you cannot complete. If you're stuck on a specific puzzle, you can give the puzzle to Watson and then farm it for another puzzle to start new.
There's also a chance of receiving the Clue Scroll drop from skilling. The probability of getting one will depend on the quality of the material that you are working with. As an example, if you are woodcutting, you will be able to collect Clue Scrolls more often from Yew trees than from regular ones. Likewise, when mining You will get more clues from Runite rock than from Iron. During skilling, you have the possibility of buy OSRS gold getting a 28.5% chance to get an Easy or Beginner Clue Scroll. 21.4% chance for Medium, 14.2% for a Hard one, and 7.1 percent chance to be Elite.