There are two ways:
1.Buy the Rainin' Lizards speedrun for 500 bones. Then just keep doing it and eating all the lizards (can also be good for the Lizard Milestone).
2.Try to find Super Eggs and achieve milestones (achievements).
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You can play easy mode
If you are looking for a easy way to install mods, someone made another Minecraft that can be used for downloading mods easier.
There is no easy way just look around for them while doing missions :)
It varies a lot on the type of bones you use. For example, with frost dragon bones it will be much faster (though also more expensive, per experience point) than with big bones. I wouldn't recommend regular bones, which are way too slow.Also, burying the bones is way too slow - and too expensive. You should seriously consider using either the ectofuntus, or - better, in my opinion - a gilded altar in a player-owned house. At runescape.wikia.com, you can find a calculator that will tell you how many bones you need, depending on various assumptions, such as the type of bone, and what boosts (such as a gilded altar) you use.
Trade for it or colonize on an island with it.