I found these (5/16"=7.9375mm) at Grainger
https://www.grainger.com/product/SOSS-Hidden-Barrel-Hinge-Without-36Y785?s_pp=false&picUrl=//static.grainger.com/rp/s/is/image/Grainger/4ACY8_AS01?$smthumb$&breadcrumbCatId=1011
And you don't have to buy 24!