Hemp shiv alternatives?

I'm looking at hemp crete as a building material. The hemp is used as an aggregate with lime. And is good for breathability and insulation. All good stuff.
I don't really want to import materials if I can, so was wondering if there was a similar plant that I could grow onsite. Or whether another shredded plant/wood would do the job. This is for an outbuilding - so happy to experiment.
I frequently have buddleia cuttings, this is quite lightweight, probably airy in structure. Also can get hold of hazel cuttings, and field maple. I'm thinking about whether I have stuff that I could use that is harvested here - general cuttings.
I'd happily grow hemp given the room if a license wasn't required, but I'd probably be hard pushed for room! Would be interested from those in the know if there is another alternative.
I could buy in some hemp shiv, but I'm looking to bulk it out.
It's a bit chicken and egg, hemp seems like such a marvellous building material, but I guess it will take time for it to catch on, and prices to fall, and for it to be grown closer to home.
But if you do know a hemp shiv producers in Sussex, Kent, or Hampshire do tell.
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