Search on Map 1-3/1-4; 3-6/3-5. Buy not more than 25 Piratekeys (Booty) --> I think this is very important... if i buy 200 key or more at the same time, i often found just bullsh...t. On De3 It was the best way to find Lf4.
The most Lf4 i get was found by IBOT... Buy 25 keys start ibot --> collect on the maps in the first line...
Good Luck