Relics of the Age of Arcanum

Relics of 2 epoch ago still persist to this day. The age of arcanum is theorized to have been a magical and fantastical era of powerful casters beyond today's capability.
Many magic items still exist from that epoch but due to a magical phenomenon called Arcanic Half-Life most of these old relics only have more one use in them before they break and no longer function.

Dangers of Relics

Due to their age and powerful magic they react poorly when together in masse.
Relic Mishaps: Every time a PC uses a relic, they must roll 1d6 and add the number of additional relics they carry to the roll. If the result is a 7+, the relic bursts with energy and the DM rolls on the spell mishap table to see the result. The spell failure table on page 140 of the Dungeon Master's Guide

Utility

Relics are one-time use magic items with a fixed spell save DC. After use many crumble to dust, while others just become mundance items.

Manufacturing

They cannot be crafted. It seems many of them are magic item that are at least 2000 years old, maybe longer.

Social Impact

Many of these relics are in the hands of merchants, or as heirloom for regular families. Noble Houses may have a dozen or so sitting around.

Access & Availability

While well known among the merchant class these items are somewhat rare making them fairly expensive. The magics used to create these items are fairly high many being between 4-7level implying that many more people of the past could use/create items of that caliber.

Discovery

The existence of these items are widely known among the people who are able to find and utilize them.
They often are found in old treasure trove discovered my exploration, and adventuring parties throughout the land.
Overtime families have hoarded these items and they have become heirlooms to said families.