I picked up a Bowen poster signed by Randy off eBay a while back, but they dont show up too often:
There's also this that Randy showed us a few months ago, but I haven't heard of any plans to release it as a poster (unfortunately):
There are full-page ads like this one produced from time to time, but I think your best bet would be to try and find some of the old Bowen advertising "flyers" that were a few pages long. They sometimes show up on eBay.
I doubt very much that you would be able to aquire any of the original montage photos sans copy.
Al, a work in progress, still looking for the right kind of shelving. I am current looking at quotes for custom cabinets. The small display area in the living room has a chance of getting a lot bigger with a room conversion of one of the kids bedrooms, just need to be patient !!