BTW, If u’re just looking for the info, and not the anecdote, its in the second paragraph 
I’ve been looking for a pair of flat bottomed grinding pedals ever since a m8 bought back Universe 2 from BJC and I saw someone using a pair to slide rails and crankland boxes. I’ve been able to crankland my onza 24" for a while now, but its always been a problem to find anything landable cos the stock pedals chew up wood and chip off stone, ruining the furniture. I’ve had to practice on a massive total of 2 different items, a metal bench in the local skatepark, and a concrete wall nearby. This has of course limited my abilities, and when I saw that a flat bottomed pedal was available I went into my local bikeshop at the first opportunity…
“Have you got any flat bottomed pedals?”
“Never heard of them!”
And this was the stock response. In 5 different bike shops, even one that sold a 20" Nimbus Training Uni (£85!) , No one had heard of a flat bottomed bike pedal. I began to despair of the mythical grinding pedals. People told me, they said “Why?, what would they be for on a normal bike?” And i had to agree, from a 2 wheeled perspective they were a bit pointless.
I had almost given up the search, until earlier today, when after a frantic weekend searching countless bike websites I found them. A pair of Gusset Full Throttles, black, £30 for www.wiggle.co.uk
“Rejoice” was heard in the streets, as I went for a ceremonious ride through my village “celebrate the day”, and so on…
So I bought them, on the spot, as well as a 20" Onza Trials (Which I was getting anyway) So now I am fully kitted out, for a new life of slides, hops and rails. All I need now is some wax…
Loosemoose