I've got two skirts from (of all places!) Marks & Spencer which were in the 'Gents' section. A 'classic' short indigo denim skirt (with 'gents' fly) which certainly fits my (overweight) shape perfectly. Marked as 20/21in, it's actually 19/20in, but there you go - I wasn't taking it back! The other was a heavy cotton version of almost identical shorts in a neutral blue-grey colour. The shorts/skirts were intermixed on both sides of the aisle! The only drawback being that although these skirts had a full, buttoned fly, it was in the 'female' direction!

Other 'mainstream' shops have had 'blokes skirts' displayed on occasion - mostly aimed at the younger element 'clubbing' on holiday. At one shop, the sales chappy said they'd been sent three 'to test the water'. They kept one on display (the buyer was going to collect a week later) and, to their total surprise, had more than a dozen enquiries. They'd enquired (obviously!), but the supplier had no more available. Sadly, they didn't go above a 30in waist!
I've seen similar (Algarve, for instance), but all aimed at the 'youth' market. I suspect this is where the habit has got to grow from. Get a few lads travelling home, thus skirted and it'll grow from there - just like casual Kilts have.