I've found this really wonderful website that has a whole bunch of these worksheets.... FOR FREE!!!!
There are a wide variety of topics and all you need to do is press the worksheets button under the section where you want to find the worksheet. This will then open a new screen where you can choose the worksheet topic which will have a riddle for your kids to uncover! These can be fun to use as small warmups/exit tickets/reviews or even worksheets to complete while you have a substitute.