안녕하세요. 최용일입니다.

그냥 위치 찾아서 하나씩 비교해보시면 될텐데요. 조금만 생각해 보시면 될텐데...

var
  Count: Integer;
  Found: Boolean;
  Index: Integer;
  P: Integer;
  Source: string;
begin
  Source := '%123%adsfgyt>ghjgdsa:sda:';
  P := Pos('>', Source);
  if P <> 0 then
  begin
    if (P - 1) < (Length(Source) - P) then
      Count := P - 1
    else
      Count := Length(Source) - P;
    Found := False;

    for Index := 1 to Count do
    begin
      if Source[P - Index] in [':', '%'] then
      begin
        ShowMessage(' Left Index: ' + IntToStr(P - Index) +
                    ' Left Char: ' + Source[P - Index]);
        Found := True;
      end;

      if Source[P + Index] in [':', '%'] then
      begin
        ShowMessage(' Right Index: ' + IntToStr(P + Index) +
                    ' Right Char: ' + Source[P + Index]);
        Found := True;
      end;

      if Found then
        Break;
    end;
  end;
end;

^^ 항상 즐코하세요...