That was my point! If you give cards out to all of the people who come across trees, whether they're tree surgeons, arborists, enviromentalists, local government employees, park wardens... and every one of them knows you're interested in getting hold of some yew, before long you're drowning in the stuff.
People have to PAY to get timber removed or stored somewhere. And along comes somebody offering to take it off their hands for nothing. Simple.