Rares are not a mysterie hehe,
It is based on luck, how ever i think the droprate fluctuate deppended on what planet you are on and and time.
But my experince as a bridgeplayer

its all about increasing your chanses
how do you do that?
The most obvious is of course the bp booster that works well when it works(i think somthing is wrong with it after latest patch)
buying E is good factor too (more time to actually shoot and kill mantis)
and dont sit and wait for mantis to spawn find a good spot where its possible to kill several groups of mantis that drop wanted gold, use AB and kill

(speed booster is very useful)
This formula has been very sucsessful for me

drops up to 13-15 gold bp evry day
Its deppended on system and ofcorse how much time evry day and how many different type of mantis you shoot.
If am after only 1 gold its maybe only 3 a day but if im looking for lets say more than 5 from that system it can be as many as 13 golds drop
