You have to purchase the first expansions of EQ (Platinum goes for the whopping price of something like $12 at a local shop due to it's age), or you can probably get it through SOE online store - though they would probably charge you for 10 other expansions they release every year without you wanting to buy them.
Alternatively, if you played EQ and have the first 6 expansions, (or was it 5? someone may have to correct me on that), and still have the folder on your old computer / portable drive (my case, since I had everything backed up on a portable drive) you can copy that folder over. There are no registry files required (EQ is cool that way) so you don't need an actual 'installation' for it. Don't bother asking if someone would host it for you though - firstly it's illegal, and secondly, as an example, my own EQ folder is about 6Gb large (though it does include several expansions and custom content not required for SoD).
Seeing as how the game is old, and I don't know where you live (I know I won't find it in a local shop here for example), you could try sites like E-Bay or your local online shop - it's probably the cheapest option if you don't already have Everquest.
You should probably edit your post. There is rule you should read that Volkier posted. I think you need the first 6 expansions. The "Titanium Edition" is what you are looking for.