Are you on bad terms with the old boss, also?  You can jump through a lot of hoops suggested here, and maybe not find out anything even by July, or you can write a short letter asking the boss if a 1099 was issued, and if so could he please send another copy, and if not, could he give you a figure on how much your client was paid.  Probably a good idea to have your client sign a statement beneath your signature saying he gives you permission to receive this information.  Enclose a stamped, self-addressed envelope.  

If you end up having to file with an estimate anyway, it would show that at least you tried.