There isn´t a place where you can get amber, but in some caves there is amber and some animals have amber too if you have the expansion pack shivering isles you can find amber in almost anything.
longsword, nowhere, but most mages guild halls have one in the open somewhere
In my own opinion the silver long sword causeit can kill ghosts
The Imperial City Guard shield would go well, and a silver longsword, or ebony longsword.
The "Gladiator's Sword" which is a longsword can be obtained by doing battle in the Arena. I do not remember the exact point that this comes up though.
A steel shortsword because they both do the same damage but a steel shortsword is swung faster.
Perfect Amber is the best but it requires the shivering Isles
any ware you can find maddnes ore or amber. there's a small chance that it will be a matrice.
Depends on what level you have it made. As you level up, higher, more powerful armor and weapons can be made from amber and madness ore. The highest quality of amber armour is even better than glass.
It is found in tree caves on gnarls and can be found in granite I don't know where that is but it is a cave in Shirvering Islises
You can buy a rune longsword at the grand exchange.
a dragon longsword changes over time but is worth around 99k
The best longsword, according to the runescape wikia, is the chaotic longsword. The chaotic longsword is obtained via the dungeoneering activity. It costs 200,000 tokens and if completely uncharged will cost 2 million coins or 200,000 coins and 20,000 tokens to recharge to 100%.