A W Jenkinson supply woodfibre but I suspect there may be minimum order i.e. large lorry load. Tracy Timber supplied the woodfibre for my arena but on googling them I find they don't appear to supply arena surfaces now. I'll be on the look out for a top up soon so let us know if you find a good supplier.
John Kind in Caldercruix supplies carpet fibre. Angus Rubber Crumb Ltd in Forfar sell 20mm rubber chips (www.rubbercrumb.co.uk) and there's also a company in Doncaster who deliver nationwide: www.goodchipequestrianrubberchippings.co.uk. Then theres is a place in Glasgow who sell playground rubber chips - it might be worthwhile checking with them what they have: Guinea Enviro, 255 Lochburn Road, Maryhill, Glasgow G20 0QQ; Tel 0843 289 6155 or 0141 946 0867.
We're still in the process of building our arena, so I haven't actually used any of these companies yet.