Hi! Can you please tell me where are these items in the game?

Silver Hilt (to join with the silver blade to create the Vorpal Sword)
Girdle of Frost Giant Strenght (piece to the Axe that gives you 25 strg)

Thanks for reading!

If you have the silver blade from the Githyanki it's only a matter of time. They will come to you and ask you for the balde; refuse and they will fight you and after you've killed em you find the hilt on the body.
The girdle of F.G. strength is in the Kuo-Tuan dungeon in the underdark
Sacrifice an animal on the statue and 5 demon lords (!) will appear which you will have to slay to get the girdle

Incidentally those demon lords are very, very tough. The only way I found to beat them was to summon everything I could - two fire elementals, a mordie's sword, and two skeleton warriors. They level drain, hit for incredible damage and cast spells like power word / symbol stun / fear.

Yep they sure are tough, but a pit fiend did for them no problem. Don't forget to cast protection from evil first though, as I found to my cost...

SuulYiin you must've been really lucky, I beat them with my group first time, but i was curious as to how a pit fiend would go against them and they pretty much minced him. They're immune to his demon fear and to a large extent his fireballs.

Stupid things kept on trying to cast horror on my mordie's sword. Ha ha ha. Anyway, I don't trust pit fiends, if they don't ignore my protection from evil they nail me with their blasted fireballs.

Thank you all for your answers! They have been very helpfull! But, alas... i am already in chapter 6... is there anyway i can get the girdle os frost giant strenght now?

Thanks once again

You can go back into the Underdark. You'll pop out somewhere in the Kuo Toa dungeon. Wander around. When you get hit by a flamestrike trap, you'll know you're on the right path.