this what ya need
There’s also a good bit of 1/4” stuff online, northern tool, harbor freight, granger etc
The name you're looking for is collet adapter.
search and take your pick
https://www.amazon.com/Grinder-Router-8-inch-Adapter-Collet/dp/B01LZI8DHK/ref=sr_1_4?ie=UTF8&qid=1501522228&sr=8-4&keywords=1%2F4+to+1%2F8+collet