ask your friends, i've done that. otherwise, you're gonna have to buy some cheap weed, or you're gonna have to suck it up and buy some seeds from a seedbank. if you only want a couple seeds then you can buy single seeds. the pick n mix site takes money orders and bank transfers if you dont want to use your credit card. i havent personally ordered from them yet, but i plan to. and its appealing that you can buy one seed at a time.
http://www.pickandmixseeds.co.uk/
and if you find seeds in a bag of crappy bud, just grow them anyway. i grew out a whole bunch of bagseed in my last grow and my 5 week old MALE LEAVES were more potent than the bud i'd been buying. its amazing the things that can happen to mary jane when she's given optimal growing conditions. some of the best bud i've smoked was stuff i grew out from crappy weed seeds