There are only 3 pieces of equipment that you need to collect for this achievement
Alucard Mail – The Alucard Mail is in the Marble Gallery upper right boss fight (thanks to Cringer85 for this info)
Alucard Sword – You get this by defeating the boss “Galamoth”
Alucard Shield - This is in the room beside the boss “Galamoth”
Boss battles can be a little tricky, have lots of food tickets and potions such as hp,defence and attack power. The battle agaisnt Galamoth took me 10-15 times but i got there in the end, try to keep combos going and get Galamoth's gems to the top of the screen so you do more damage.