Being careful and trying not to embarrass myself, have you googled the item, searched on E-Bay and Amazon?
I was looking for some a few years back (didn't buy in the end) and found plenty of information about them and installing them. At the time I was looking at the 40 - 48mm deep ones, just because a heavy(ish) van would be parked on them and I thought they'd be better, no other reason.