I’ve already found the store. They get most of they beanies at Zumiez and they have at least one from River Island.
Here are some of the beanies:
Blue Ribbed Knit Beanie Hat – £6.40 (On Sale) by River Island
Neff Daily Cyan & Black Beanie – $18.95 by Zumiez
Brixton Abbey Coral Beanie – $19.99 by Zumiez
Neff Daily Fold Magenta Beanie – $17.95 by Zumiez
Neff Daily Pink Beanie – $17.95 by Zumiez
Neff Daily Yellow Beanie – $17.95 by Zumiez
I also found these two beanies. I saw R5 wearing them sometime ago.
Aperture Pedro Lime Slouch Beanie – $16.95 by Zumiez
Aperture Pedro Cyan Slouch Beanie – $16.95 by Zumiez
The yellow beanie above was not matched correctly, as you can tell from the patch, but you can find the exact here.
But other than that, this post is spot on! 