Giving thief to Drifloon and giving it nothing to steal seems mean.

Burmy may be holding:

• Rabuta Berry - 10%
• Charti Berry - 25%

Pineco may be holding

• Oran Cherry - 10%

Phantump may be holding

• Nomel Berry - 10%

Shedinja may be holding

• Black Lotus (This is not a real held item, and in 1.16.5 it won't be added to the Shedinja)
• Kelpsy Berry - 50%

It is unclear whether or not these held items will actually be held by Pokemon that come from spawners. Untested.

Pokemon that come from spawners DO NOT naturally hold any items. However, you can get them to hold items by putting in a more complete 'name' for them. For instance, a spawner that spawns burmy helditem:oran_berry will always spawn burmy with a held oran_berry. Weighting can be used.

Worked.