I got mine from Insulation Express Insulation Express | Specialists in Insulation and Building products
They are an online outlet for Sheffield Insulation. SI have lots of local outlets that they've bought up over the years and their big warehouses of course. Prices can be different at the various outlets. If you buy lots then you might be better with an account at SI themselves.
Are you from Sheffield IHB?
I'll have to look into it, if I can make a bit of money on the side then happy days