If you have source code license, you can try to compile it for Delphi 10.
As a quick workaround, you can change sDefs.inc and add two lines:
{$IFDEF VER300} {$DEFINE DELPHI_10} {$ENDIF}
{$IFDEF VER290} {$DEFINE DELPHI_XE8} {$ENDIF}
…
{$IFDEF DELPHI_10} {$DEFINE DELPHI_XE8} {$ENDIF}
{$IFDEF DELPHI_XE8} {$DEFINE DELPHI_XE7} {$ENDIF}
…
After that, you can use the packages from the previous version acntDelphiXE8…
I was able to compile and use AlphaSkins under Delphi 10 Seattle. But I didn't test it on bigger projects. Maybe there are hidden bugs needing changes to the source code.