Two questions a) if you don't have access to willow trees (I live in South London and because of subsidence it is not very popular here) can you make it.
b) If not can you buy it from Wilkinson's? Online seems quite expensive and we are not that near any garden centers?
Yes you can buy it from wilko's and it cost only about £1 or so. Not worth of hassle doing it yourself.
I'm not convinced about doing it yourself job anyway... :-\