Ring of Regeneration
Ring, Major, Very Rare (Requires Attunement)
While wearing this ring, you regain 1d6 hit points every 10 minutes, provided that you have at least 1 hit point. If you lose a body part, the ring causes the missing part to regrow and return to full functionality after 1d6+1 days if you have at least 1 hit point the whole time.
Source: Dungeon Master's Guide, page 191
Ioun Stone, Regeneration
Wondrous Item, Major, Legendary (Requires Attunement)
[Removed unrelated effects.]
You regain 15 hit points at the end of each hour this pearly white spindle orbits your head, provided that you have at least 1 hit point.
Source: Dungeon Master's Guide, page 176
Hand of Vecna
Wondrous Item, Artifact (Requires Attunement)
[Remove full item description.]
Properties of the Eye and Hand. If you are attuned to both the hand and eye, you gain the following additional benefits:
- [Removed unrelated effects.]
- If you start your turn with at least 1 hit point, you regain 1d10 hit points.
Source: Dungeon Master's Guide, page 224
The above items give you something weaker than monster regeneration (which can be upwards of 10 HP every round, usually 20). As far as I'm aware, there's no official item which gives Regeneration of that grade to anyone. The closest you'll get is 1d10 HP every round with the Hand of Vecna, and only if you attune the Eye of Vecna as well. Both of which are Artifacts of the highest rarity, body parts of one of D&D's most-famous Liches.