I started with getting scans of cardbacks with the bubble cut off, still leaving the bubble "Flange", and using photoshop (or gimp, a free one), to restore it to it's former glory. I recently got my hands on these scans which you can download for free. I ended up paying a pretty penny to buy a couple of disks with them on.
Here's a link to the downloads.
http://smg.photobucket.com/albums/v729/ ... ans/82-83/
here's an example:

I then bought the crimson guard blister from here:
http://www.guardian-dragon.com/gdp-repro-us.htm
and made this:

I used bostick sticky sheets to attach the blister as this leaves a similar effect to the original process used in the factory.
The cardbacks themselves can be used to create a blank template for creating your own cardbacks
Here's a link to artwork used for the cardbacks. I used the scarlett art, removed the figure, and restored it to a blank explosion. This can then be used for custom cardbacks.
http://www.joebattlelines.com/m6d/ArtofGIJoe/1983.html
You can use the crimson guard blister for a few of the characters, namely, cobra soldier, officer and cobra commander. I think it would also work with flash.
Hope this little piece of info helps.