I have found that iNaturalist can be a good resource when doing research for this thread. Here are some that have been introduced, but don't have any sightings.
Cane Toads in China.
China · iNaturalist
African Clawed Frogs in Indonesia.
Indonesia · iNaturalist
Muskrats and Lesser Antillean Whistling Frogs in Brazil.
Brazil · iNaturalist
American Bullfrogs in Russia.
Russia · iNaturalist
Red-whiskered Bulbul, Red-vented Bulbul, Alpine Ibex, Crested Myna, Rosy Starling, Red-breasted Parakeet, Alexandrine Parakeet, Aldabra, Giant Tortoise, Nubian Ibex, Zebra Waxbill, Senegal Chameleon, Marbled Water Monitor, Western Green Mamba, and Jameson's Mamba in Mexico.
Mexico · iNaturalist
African Clawed Frogs in Japan.
Japan · iNaturalist
Reeves's Muntjacs in France.
France · iNaturalist
Italian Crested Newts, and African Clawed Frogs in the United Kingdom.
United Kingdom · iNaturalist
American Bullfrogs and Vervet Monkeys in Thailand.
Thailand · iNaturalist
Pallas' Squirrel, Indian Crested Porcupine, Javelin Sand Boa, and Albanian Water Frog in Italy.
Italy · iNaturalist