While in iRule Builder, so a search for the buttom type you want. Just typing [stainless] will get you a good start. From the iBuilder search folders you can drag & drop into your folder/desktop. You can not drag & drop from the image folders within your active Builder 'application,' it must be from the search folder. (that's where I had trouble at first).
Next drag the button from your desktop, etc to the paint program of choice. Paint dot net is free & works very well. Keep an eye on the size of the pics. You can resize in Paint which allows you to be more accurate in your placement on your page. Good luck.