The easiest place to get runes would be the grand exchange in varrock, but can also be purchased at mage stores. Look for the symbol on the map for locations.
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Buy Them at the grand exchange, craft them, or buy them from the mage guild.
First you have to buy runes. you can buy runes in Varrock and you practice your magic buy killing many creatures with mage. or you can buy magic tablets in the GE if you dont want to carry around all those runes
To get runes, you can either buy them from the various magic shops around Runescape, on the Grand Exchange, or make them from rune essence and pure essence at the runecrafting altars hidden around runescape. If you need help, my runescape username is Xeyran.
lvl 70 wc buy a ton of runes
as of October 4, 2012 a blood rune is worth 278 coins.
In the Grand Exchange, you can buy Mind Runes for 8gp right now. It may be a little more expensive to buy them in a shop.
go to every mage and fishing shop every day and buy all the water runes and earth runes and fethers
You can make the at the water altar, buy them from a rune shop, or buy them from the Grand Exchange.
Mostly Fire runes but Law runes and Air runes are not far behind them.
The best way to obtain runes in RuneScape is through the Grand Exchange as you can buy runes for bulk there quite efficiently and for a good price. Another option is buying runes from RuneScape stores, which usually will offer the cheapest prices but also a limited stock. The best stores to by runes in RuneScape from are from Aubury's shop in Varrock and the Magic Guild in Yanille. Runes can also be obtained from Thieving and practicing combat skills, but will take a lot of time because of the various drops possible. If you feel like you want to get a lot of experience, then making the runes yourself is the best option as it is easy. However, it is a very time consuming process and is usually easier to just buy the runes from the Grand Exchange.
Fire runes are over-produced on RuneScape, so there are far more on the market than people willing to buy them. However, they will sell if given enough time.