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.
You need the Shivering Isles. In the city of Bliss, there is a guy who can make it for you, the stores' name is "the missing pauldron". You have to collect so many pieces of amber for each different part. You'd need at least 30 pieces of amber to create the whole suit of armor and weapons too.
You need the Shivering Isles expansion, a smith in Bliss makes them.
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.
A steel shortsword because they both do the same damage but a steel shortsword is swung faster.
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.
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%.