Featherproof inner covers for cushions and pillows used to be quite common, but have become rarer due to the use of fibre fillings. These days such materials are still found on feather duvets.
Ask in the bedding department of any large department store - a knowledgeable assistant may be able to help.
I have had this problem - I find it better if I use another pillowcase/cushion cover underneath - so that the spikey feathers can't get though so easily!