I am looking for embroidery patterns that I can use on material that I already have

You might take a peek at Beth Russell's needlepoint books - these have charted patterns of her interpretations of many William Morris textiles. also, the Caron website has an embroidery pattern based on Morris' work, i think by Ann Caswell.
Best of luck!

If you can draw and know embroidery stitches well, you might want to consider just having a look at photos of embroidered pieces in books on Arts and Crafts and tracing them on your fabric - you might get inspiration from other textiles and ceramics too. I know I've seen several I'd like to try (but I don't embroider )

Hello Ginny:
I might be able to help you by offering my services
for drawing up authentic motifs for you.

I have a vast collection of A & C motifs that I could possibly custom design for your use.

If I can be of any help, please email me at studio@terrafirmalinens.com

All the best,
Linda

Take a look at this thread for ideas. There are lots of images for inspiration.

Arts and Crafts Embroidery on Linen

Lauren