Leveling help

Hi, i just picked the game like a week ago.
I'm aiming for TbXie's Unkillable Necro - Detonate Dead Necromancer Build
https://www.poe-vault.com/guides/unkillable-necro-detonate-dead-necromancer-build-guide

I'm stuck at section 10.2 due to:
1.- being unable to find these support gems:
Controlled Destruction Support
Elemental Focus Support
2.- Even if I find all the gems I would need an item with 4 slots and 4 links to be able to use the gems, right?

also, the leveling part of the guide doesn't specify what to do with frost bomb/onslaught/added lightning.

thx in advance for any help you can provide

edit: I just started act 2

Hi and welcome to PoE!

You get access to both Controlled Destruction and Elemental Focus after killing the weaver in the Western Forrest in the Sharp and Cruel quest.

Yes, you will need an item with 4 linked sockets to be able use all the supports. Check the vendor (Greust) each time you get back to the Forrest Encampment to see if you get lucky with a 4 link item although 4 links only really start showing up from Act 3 onwards, and can then still be rare.

Link Frost Bomb with Onslaught and Added Lightning. Then drop Frost Bombs as you fight to help with tough mobs and bosses.

I would suggest you pick up a Herald of Thunder from the Intruders in Black quest to use along with your Storm Brand. Also use Skitterbots which you unlock from Yeena after completing The Root of the Problem.

Thanks for the answer and apologies for not being more specific.
The guide says that after reaching level 12 and killing Merveil I should setup:
Storm Brand
Added Lightning Damage Support
Controlled Destruction Support
Elemental Focus Support

I was wondering if this should replace frost bomb/onslaught/added lightning or storm brand is meant to be used along frost bomb... like drop frost bomb then drop storm brand and fill with another spell (like the one you mention)

Again, thanks so much for taking time to answer

No problem :)

You should use Storm Brand as your main damage dealing skill and use Frost bomb as a more supportive secondary skill.

The cold damage from Frost Bomb will slow enemies down as well as reduce their Health and Energy Shield regeneration.

During boss fights the Onslaught support skill will grant you the Onslaught Buff when Frost Bomb hits the boss. (Onslaught Grants 20% increased Attack, Cast and Movement Speed)

The Herald of Thunder and Skitterbots will also act as support skills for both Storm Brand and Frost Bomb. Herald of Thunder will increase your damage, acting like and additional 'Added Lightning Damage Support' gem to all your skills.

Skitterbots are 2 little minions that run around applying 'chilled' and 'shocked' status effects to mobs. Chilled effect slows down enemies and works along with Frost Bomb. Shocked effect causes enemies to take more damage, allowing Storm Brand to do more damage.

Thank you very much for the detailed answer. I'll adjust my build according your recommendations