1. Uraninite

Try to buy Uraninite (formerly pitchblende) at a mineral show. I bought some pieces of Uraninite from the famous formerly Russian uranium mine of Hartenstein, Saxony, Germany, at an internet mineral show. Uraninite contains up to 88% uranium. Uranium is weakly radioactive because all its isotopes are unstable. Below video shows the radiation measurement with a GAMMA-SCOUT Geiger counter.

2. 241-Am

The most common Americium isotope ²⁴¹Am can be obtained from an ionization smoke alarm. The isotope has has a half-life of 432.2 years. ²⁴¹Am decays mainly via alpha decay, with a weak gamma ray product:

Next figure shows a dismantled Ei100L smoke alarm. The red, round structure at the right is the ionization chamber.

The washer shaped part in the middle of the lower electrode of the ionization chamber contains the ²⁴¹Am. It has an activity of 33kBq.

Trimmed ²⁴¹Am source soldered onto the brass disc described here. Make sure, the alpha particle emitting side points to the center of the brass disc.