i am a joiner and we get several people come in weekly to pick up shavings we keep in a skip outside, there are several woods mixed in mainly oak and ash though and from what i have heard they work a treat so maybe try your local joiners shop just make sure that there will not be high amounts of \MDF or tanalised timbers!! doesnt make for tasty bacon! i am sure they would be more than happy to give them away as it saves them having to pay for removal!!!