Finding large quantities of chopped bark to add to bonsai soil mixes has long been problematic in the UK. Until recently only bales of large pieces of bark have been widely available. Sifting through a bale of such bark could leave the enthusiast with only a few handfuls of usuable material (pieces of bark up to 8-10mm in length).
However, there is now a newly available product called 'Decorative Mini Bark' by Westland, sold in 80 litre bales and available at many garden centres including the Wyvale's chain, retailing at around £6.00.
After sifting one of these bales through a 10mm mesh, I had 40 litres of bark suitable for my bonsai soil. A definite improvement on previous products!
(Unsifted) Mini-Chopped Bark for bonsai soil mixes.
Francis Consunji-Chan, a member of the Wessex Bonsai Society tells me about another source for pine bark. In Bournemouth (UK), Roffeys ltd sell Melcourt Pine-bark which is available in a number of grades but for bonsai purposes, the propagating grade is best. They offer a 75 litre bag for around approximately £13 and the particle size is such that it does not require sifting prior to use in bonsai soil.
Melcourt Pine-bark; propagating-grade