Talisman of the Hearthfire - Baldur's Gate 2 Side Quest
Talisman of the Hearthfire is a side quest that begins by speaking with Knocktor the Fizzled in the Hidden Refuge camp. The Hidden Refuge zone is part of the Enhanced Edition for Baldur's Gate 2 and can only be accessed after progressing far enough in Neera's Companion Quest. You will also have to recruit Neera into your party to access the Hidden Refuge.
All you have to do for this quest is find 2 Diamonds and 1 Silver Necklace. Diamonds are going to be the harder item to find since they don't drop off enemies and there are only about a dozen or so in total throughout the whole game. Silver Necklaces are common drops off of low level enemies since it's standard vendor trash.
One thing that may help you out is to visit all vendors you've previously sold items to and check to see if they have Diamonds or Silver Necklaces. When you vendor an item in this game it will stay on the vendor indefinitely so you can simply return and buy back whatever you need.
If that doesn't work for you then I have compiled a list below of the different places in the game you can get a Diamond or a Silver Necklace.
1. Dropped by Lehtinan in the Copper Coronet
2. Found in a Cart near Quaid in the Wild Forest
3. Inside a container in the Navigator's Room of Planar Sphere
4. Umar Cave in Umar Hills; after killing the mimic loot the chest
5. With Haer'Dalis in your party talk to Samuel Thunderburp in the Five Flagons Inn of Bridge District
6. Talk with Guildmistress Busya in Trademeet after completing Dealing with the Trademeet Genies
7. Crate near Renal Bloodscalp in the Shadow Thief Guild located in Docks District
Silver Necklace Locations:
1. Derelict House in the Bridge District; search the painting on the wall that's a container
2. Pick pocket guards in Athkatla, Silver Necklace is a somewhat common Pick Pocket
3. Visit the Temple Sewers and spam sleep; Goblins that attack you will drop Silver Necklaces
4. Visit Windspear Hills Dungeon and spam sleep; enemies you defeat will drop Silver Necklaces
Don't feel like running around all over the place looking for these specific items? Below are the console commands for Silver Necklace and Diamond so you can instantly create them and complete this silly quest without any frustration.
Once you have the required items return to Knocktor the Fizzled and give them to him along with 3k Gold and he'll give you Talisman of the Hearthfire along with complete your quest.