Lee Burnett

I've got my first set of redhead lights (not the cheapo ebay ones) - wanting to start experimenting with diffusing, flagging, bouncing etc. I've been looking around for somewhere to buy diffusion sheets in the UK but struggling to find somewhere that seems legit and sells everything. Can anyone advise? Also, if anyone has some advice or links to videos to help me build my own diffusion frames, that would be sweet.