Does anyone know where I can get a tapestry or embroidery set...

[reastie]

..with a fern pattern on?

not this one and, if possible, as similar in style to the fern material here as we are using the material in our room and I'd like to make a fern cushion to coordinate everything together.

First link didn't work of initial kit I didn't want so trying to relink here

There's a green version - no good?

No, I just don't like the design I'm afraid, want something more similar to the material linked above.

Can you embroider freehand? If so, try taking a swatch of the fabric into JL or Hobbycraft and picking out the colours you'd need yourself. That way, using squared paper (or even a photocopier) you could adjust the size of the motif you want for your cushion to be exactly what you want.