Crooch, have a look on chainreactioncycles.com as I saw them on there.
They're just knee pads though, not knee and shin. If you want knee and shin I'd suggest the Race Face Rally FR (if they still make them) as they tend to stay in place in a crash. Not sure whether they would fit under race pants though. If you go for Dainese, also invest in some 661 Pad Locks to keep them in place when you crash!