I've just dug out that link (packed with other good links) out of several with 'bent to the bonny broom' part to give you a start. It might help if the subject could be focused a bit differently. You can post a request here for a moderator to help with changing the subject a wee bit if you wish to do so.

If I have any time later this weekend I'll do some more digging for fish, stone, deer, and oak used in conjunction with bent and broom. And it's a riddle song...you might try looking up riddle in the DT.

Could you perhaps give us some more information, please? Where you know it from, who might have sung it and where, etc.