Gentoo's package manager (ebuilds) installs only a few Squid releases. It does not support 3.5 patch releases or Squid 4 beta.
I customized Gentoo's Squid "ebuild" to support the latter. It was working fine while www.squid-cache.org named the archives with integers in the patch "release" version.
eg. I could install custom versions with these ebuilds:
squid-3.5.26_p2017070214182.ebuild -> grabbed Squid 3.5.26, patch 20170702 r14182 (assuming the latter always starts with 'r')