I know you've probably heard this a hundred times, but you really can find the coolest stuff at antique malls, thrift stores, flea markets, and garage sales. They're ESPECIALLY a goldmine for trinkets and signage, in my experience.
Mercari and Depop are also fun secondhand marketplaces, you just have to know what you're looking for.
Also consider local listings on Facebook marketplace or Craigslist.
Outside of secondhand, you might look into Etsy, Spencer's Gifts, Target's dollar spot/seasonal stock, or your local dollar stores.
It helps me to use the keywords "kitschy," "fun," "funny," or "funky" when searching for inspiration.
Some of my favorite finds lately:
•Russian nesting doll measuring cups
•Dancing Frankenstein doll
•1970s childrens bookbag made to look like the Barnum's animal cracker box (I use it as a laptop case)
•Pillow with Andrew Garfield's face printed all over it
•Floormats deisgned to look like your favorite DVD/CD/game disc
(As a disclaimer, I admittedly don't know much about the ethics or international shipping policies of any of the aforementioned companies.)