i am up tp 57 things but how do you get more? i find one occasionally at the desert but mostly i get clay and seeds.
Minerals and gems make up over half of the museum collection, so mining for geodes is a reliable way to make donations. Also quartz and the others on the ground in the mines.
Some artifacts drop as loot from monsters, especially skeletons and coal sprites. You can also find artifacts by digging with your hoe in dirt floor areas in the mines. You can dig up all the dirt, leave so it resets, and go back and dig it all up again.
Different artifacts can be found digging wriggly worm spots in certain areas of the map. For instance, there's a gold mask and gold relic found in the desert. Some will only be in the forest, or town, or the farm. You find the most worm spots in winter. I do a lap of the map, checking everywhere like the beach, spring onion place, secret woods, bus stop, railroad, quarry.
Fishing up chests sometimes gives artifacts. You can also get artifact troves, I think from the desert trader.