I'm going to steal that diorama. Just FYI.
You can try, but it would probably be easier and friendlier to just buy one on Ebay. A couple: here, and here.
Although no matter how much I look I can't find one that corresponds to mine directly. The text at the bottom saying "Thy Kingdom Come" and "100 Days Indulgence" is different on others, as well as the background picture and the various pieces. The others tend to look like the two I linked above, with much smaller variations like colors etc. And in case anyone is interested, these shadowboxes were originally made to honor Pope Piux IX's 50th anniversary in 1877 since his ordination (as a bishop, I believe).
A couple years later and I still can't believe I picked this up at a flea market for less than $20.