Do you have a link for magnetic stick-ons? Thanks.
staples, office max, etc. all have magnetic tape in varying sizes.
any variety store (most any) carry magnets you can cut to size with a sticky side.
Suppose to be for pictures that you want to put on the fridge or whatever but they would work great for the bumper sticker and very affordable...they come in a multi pak.
Most sign shops carry magnetic sheets for making those signs you see on some service trucks. I used the magnetic refrigerator football schedules we get every year. I still have the oval W 04 on my riding mower.
Now, I made similar ones with the red slash through the O and OBAMA stickers. I get plenty of #1 driver gestures in Austin.