I "worked" (played) damn hard to get all in-game rares. Paid hard cash for boosters and extra e as well. I resent that finding rares should be made easier. You want them? Put in the effort! Find a method (there are several). With the exception of some rares (MMB, SSB for example) rares will drop from ANY rank mantis. In these cases don't go for higher level, it does not guarantee more chace of a rare drop. Choose a planet where there is a lot of activity (more players=more kills=more bp drops=higher chance of rare drop). The negative side of this means that it may not drop for you (there is the luck factor). Alternatively, choose a planet with little activity, stock up on e, hold your station and kill like crazy.
Don't forget to relog occasionally. It DOES help.
In the early stages of rare hunting choose a spot where you can kill several mantis types to increase the chances of a rare drop. Only later in-game when you are looking for those that you have missed does it become more random and therefore more frustrating (especially in cases where 1 particular mantis type drops a variety of rares).
If you think this is just make-believe here is a case in point. Last night between cq's (45 mins) i was asked by a clan-mate to help find Mizar Thermo. My first ds kill dropped Mizar rockets (in all likelihood someone had been bashing away all day for them so the luck factor was there. My squad member had orbitted and was heading for cq while I decided to push it to the limit. Bingo. Mizar Thermo. Persistence pays (and of course a booster helps

I remember myself, the Hyper boys, Agent007 (to name but a few) were hunting incessantly for gemini perforator only to determine that it had been omitted from the game. Once rectified it dropped easily.
Remember, the higher the system, the harder the rare.
http://www.google.co.uk/search?hl=en&defl=en&q=define:rare&sa=X&ei=sGjaTInMLtCVswaB_ZSSCA&ved=0CBUQkAE
The link above will give you a precise definition of rare. Nuff said.
And a little known fact, if you drop an unwanted rare and do not collect it then your chances of dropping more are reduced because you have waved two fingers at Fate, Luck and the Gods of Gold (actually that's not true but a supersticion of mine...lol)