Pieces of wood to fix raised bed (PL4 Greenbank)

My dad helps run the Friends of Freedom Fields park and they have some raised beds some of which are falling apart.

We've been patching them up over the year with random pieces of wood but we don't have any large enough to fix the bed shown in provided photos.

The measurements for the part we need to fix are:
Length 109cm
Height 46cm

The thickness of the wood the beds are made of are 4cm but the replacement wood doesn't necessarily need to be the same thickness.

If anyone has anything they don't mind us having we'd be very grateful. It dosen't need to be a single piece as we could place two pieces on top of each other.

Assuming your not too far away we can come to collect it. Our postcode area is PL4.

Thanks you.