This is a great source of wooden crates that make great raised beds, if you are just starting out. They are art packing crates and come in all sorts of shapes and sizes. They make quite thin walls for raised beds but they can be a great way to start out, and walls can be reinforced over time.

https://www.facebook.com/martinspeedrecycling/

Because our soil is so poor we do recommend growing veg in raised beds, and buying in soil to fill them. This is the most costly part of starting a community garden.

Sometimes you can get topsoil from building projects. Look out for someone digging out their basement!

And of course you can supplement this with home-made compost. Generally our community gardens do a bit of composting but it is something we could be much better - and faster - at. IEL has run some training in the past. Is this something we should do more of? If you are good at composting can you share? Can we facilitate some visits/sharing?

If you're lacking volume of material, have you tried mixing autumn leaves with mown grass for composting? There's plenty about at the right time of year, and the combination of the wet grass and the dry leaves should make for reasonable decomposition if you mix them well enough. 

Clarkshaws brewery in Loughborough Junction has hop waste that is great for composting

https://www.backyardgardener.com/garden-tip-articles/garden-guide/hops-and-mushrooms-as-compost-manure/

Sue