Titiritero
Retro Guru
An easier although not as nice option is what my brother in-law does in his German cycle-touring forum. They create each year a wall calendar with the best 12 submissions (here could be the last 12 "bikes of the month"). I don't know the exact logistics, if you need to pre-order and someone does the bulk order and then post individually, or they just upload the template somewhere and you just place your own order. I can ask if interested...