I have purchased the Dungeon Masters core rule book but don't have access to the Sword of Vengeance or it's child variations on any character sheets. Any one else experiencing this issue?

Can you access this: https://www.dndbeyond.com/magic-items/5505-sword-of-vengeance

 Note that "Sword of Vengeance" isn't in the inventory.

• Glaive of Vengeance
• Greatsword of Vengeance
• Longsword of Vengeance
• Rapier of Vengeance
• Scimitar of Vengeance
• Shortsword of Vengeance

Yeah I can access the article about it, but none of the weapons associated with it as you listed, appear in the inventory to be added.

What are your character's "Sources" set to in the Character Preferences?  I can only get the entry to go away if both the Core Rules and the 2014 Core Rules are turned off.

I have all sources turned on and it wont appear.

Also if I try to copy it in the homebrew I get a 403 Forbidden error: "As you try to enter the 403rd level of the endless dungeon, the ancient dragon Rylzrayrth rises up to block your path. The dragon has forbidden you from traveling any further."

This only seems to affect this one weapon type from the DM Guide. I can add "Enspelled" or "of Warning" weapons and copy them in homebrew without issues. Just "Of Vengeance" seems to be broken.

Any progress on this?

I can add all the vengeance variants to a character just fine.

I can't. When I click on one of the links Perringarden posted above, it takes me to the marketplace page for the 2024 DMG, even though I already own it.

And also, when I go to https://www.dndbeyond.com/magic-items and search for the Sword of Vengeance, it tells me I must buy the DMG, which is already in my library.

Have you checked your licenses are in sync? https://www.dndbeyond.com/account/licenses

i have also had the same issue, i have reported to the support email  in august and they have said it is not an issue my end, also same issue with tome of the stilled tongue.

Their reply:
Thank you for emailing us back. We appreciate you reporting this bug and we have escalated it to the appropriate teams to be investigated further. While we are unable to provide further updates at this time, please keep an eye on our changelog here for updates and fixes to D&D Beyond.

At least it's not just me. I ended up putting in a ticket as well.

Licenses are in sync. 

I went into DMG on the browser and moused over the item's title, only to get a black pop up that says “This content is part of the Dungeon Master's Guide Digital Content Pack…”

But I don't get that on, for example, the Sylvan Talon, which is just a couple of paragraphs down. I am able to see all the variations/derivatives of the Talon.

having the same issue

Same issue here. Sent a ticket about it.