Hello, I'm making a warlock character and I'm trying to make the Eldritch Blast as strong as I can using Eldritch Invocations, however something is off:
I can see the invocations Agonizing Blast and Repelling Blast, but I can't see any of the other blast invocations. Do I have to buy these? If so I haven't been able to find what sourcebook they are in. Any help is appreciated, thank you.

If you search for "Warlock Guide" on Google, they usually post the sources with the content. Most of them are in the Players Handbook, including the two you can see.

For troubleshooting, make a 20th level warlock and see what becomes available. If you get more options, then the problem is probably with your character settings.

The only three invocations that impact Eldritch Blast are Agonizing Blast, Eldritch Spear and Repelling Blast, with all of those appearing in the PHB.

I'm looking for things like Twisted Blast, Corrupted Blast, ect.

Setting the character to level 20 didn't work, and when I searched Warlock Guide I couldn't find anything about Twisted Blast or Corrupted Blast, so I'm going to assume that they are probably homebrew or something, so I'll just use different invocations. Thank you for your help.

Yeah, those sound like homebrew.

Lance of lethargy is the only one I see that Seasoning missed.

Edit*  Also grasp of hadar