Pressure regulators are available from most good plumbing supply houses (including some of the very big hardware chain stores)..... what you want is a 350kpa regulator (approximately 3.5 Bar)..... expect to pay around $100 for one of these....
Water softeners for coffee machines come in two main varieties.... cartridge and ion exchange. The cartridge has to be replaced fairly frequently - and is expensive..... the ion exchange (which most cafes use) is recharged every couple of months with a kilo of cooking salt.... ongoing costs being minimal.... but both work very well.
If you are interested in the ion exchange units (a stainless steel cylinder with a couple of taps) check out commercial machine repairers etc.... they often have second hand units for sale at a good price.
As far as taste.... little effect but what there is is generally beneficial..... Unless you go to a RO water softener.... coffee needs some water hardness for best taste and the RO units remove all the hardness (and can also stop the level sensor working).... RO units are also expensive.... so stay away from them!!!!!!