where can i find rune longswords?

Some shops like Champion's Guild sells them, but it's easier and cheaper just to buy them from other players.

 

 

 

Or do you mean monster drops?

I'd like to point out one thing, misleading titles aren't very acceptable. :shame:

 

 

 

Italic means members only.

 

Anyway back to topic:

 

 

 

They can be bought from the Champions' Guild for something between 30k-35k. (sorry don't remember)

 

 

 

If you are more of a fighter go to Brimhaven Dungeon, get prepared with 20 sharks (even tunas will do), armour(rune could work) and 3 antifire potions and you can kill red dragons. Trust me it is common. Don't forget to bring something to teleport away. I doubt you would survive by walking back after long fight against red dragons.