There's only one person you can buy art from - Redd.
Redd's ship is the only location to buy art and statues and he only appears at certain times; meaning it can take some time to finish off your collection.
For most, he will only allow you to buy one piece of art per visit - but that's not actually true, there is a way around this!
Here's how you can buy more art from Redd in Animal Crossing New Horizons
How To Buy More Art In Animal Crossing New Horizons
Animal Crossing New Horizons only allows you to buy one piece of art a day from Redd.
However, there are ways around this to buy more. Instead of one piece a day, it's actually one per villager.
If you create additional Islanders you can buy more art from Redd and fill up your art gallery faster.
You can buy up to four pieces, per day, using this method!
Be sure to check out all of the art in Animal Crossing New Horizons so you can be sure not to buy duplicates.