Yes of course I realize this. There is no list of 'no apparent motive recent shootings' on wikipedia i'm afraid, so you will have to do a little leg-work yourself.
Feel free to scan through the US list and pick out the many dozens that fit. Just reading down the top of the list, in the last decade or two I see Tuscon 2011, Geneva County massacre 2009, Cupertino quarry shooting 2009, Oikos University shooting 2012, Seal Beach shooting 2011, Aurora shooting 2012, Columbine 1999, Brown's Chicken massacre 1993, Northern Illinois University shooting 2008. That's from the first 4 or 5 states in that list.
There has been exactly three massacres of this type in recent UK history (~last 50 years). There are dozens in the US just in the last couple of decades. So implying that UK has a similar incidence of random killing spree gun crime as the grandparent did is disingenuous.