Glad it’s not only me who’s finding locating the bargain berths a nightmare!
As with others, it used to be so simple – if you had a specific date you could use the ordinary booking system, if you had a rough idea but were keener on price, then you could use the Bargain berth.
(Interestingly, most [granted, not all] airlines show you the min price for the days around your trip if you have flexibility.)