The odds of getting a motorcycle for free that's in very good condition are pretty high against it happening, but it's not impossible; we can think of a few ways you might be able to get one for free, or nearly free.
Check around at any local motorcycle repair shops and ask if they have any that are too beat-up to resell. See if they'd just give it to you to get it off of their property. With some online studying and a bit of elbow grease you might be able to restore it.
Another option is to search Craigslist, or eBay; sometimes you'll find someone willing to trade an old bike for some other type of merchandise that you have and no longer want, maybe a guitar, or some old furniture.
Sometimes you can get lucky and find an old junker parked in someone's driveway, or tucked along the side of a house and you can suggest that you'd like to make a project out of fixing it up and restoring it if they'll let you take it.