I did think if chopping bits off the end of something like a rear valance could get you a head start, but it could be a tad pricey. I've do have a wok, but no Mini saloon to pattern match it to 
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It also occurred to me that a female former would likely work better as you'd be tin bashing into thin air to stretch it - Care needed to prevent the edges buckling, an oversized bit of sheet and/or some clamping.
