MH,
This outfit seems to get high marks. Haven't used them myself but I see people say positive things:
Sheppard Air Flight Test 5.0 Prep Software ATP, Flight Engineer, Mil Comp - FAA Airline Transport Pilot
And at the risk of telling you something you already know, to take the ATP(ME) written you'll need the ATP-CTP course. Another wad o'money there unless an employer provides it for you.
Best wishes to you on your undertaking.