https://www.gnu.org/licenses/gpl-faq.en.html#DoesTheGPLAllowDownloadFeeDoes the GPL allow me to charge a fee for downloading the program from my distribution site? (#DoesTheGPLAllowDownloadFee)
Yes. You can charge any fee you wish for distributing a copy of the program. If you distribute binaries by download, you must provide equivalent access to download the sourcetherefore, the fee to download source may not be greater than the fee to download the binary.
The binary is distributed freely, so.. Where do we get the source code?

ps. verbatim means the original unmodified version
but you can actually distribute modified version for a price or for free, as long as the source is provided
The same is for modified sources:
5. Conveying Modified Source Versions.
You may convey a work based on the Program, or the modifications to
produce it from the Program, in the form of source code
under the
terms of section 4, .....
Anyway I have no problem to distribuite the source code if someone asks for it.
Give me an address and I'll mail the kernel's.