http://www.ebay.co.uk/itm/like/131119403241?limghlpsr=true&hlpv=2&ops=true&viphx=1&hlpht=true&lpid=108&device=m&adtype=pla&crdt=0&ff3=1&ff11=ICEP3.0.0&ff12=67&ff13=80&ff14=108 ... Just saying
Not too hard, I used a dental drill but you can use a dremmal. They're 6x9s but the grills are bigger than the speaker do I had to cut around the outside of the parcel shelf to make them fit.
Got a grommet off eBay for 99p. Its a 32mm grommet but the hole is 30mm, it fits fine but domes slightly so nothing noticeable. So if you're looking and can't find a grommet the exact size, one slightly bigger will work fine
Got the single grill done today.
Grill mesh arrived, cut out a cardboard template, gut out the grill mesh and installed it.
Pleased to say that I'm am one of the few owners now with a facelift k11 with a single grill/ open mouth.