They have an official online store now.
While I probably wont be buying anything from them anytime soon (the yen euro exchange rate is a big factor in that) I would probably go for the letter opener first since it looks cooler than the pair of scissors I currently use. When I was in Rome I didn’t buy anything Swiss Guard related I was just happy to see the real guards and take photos. It may depend on the guard, or for security reasons but the one I asked would not permit me to have my photo taken next to him. I felt uncomfortable asking in the first place since they are on duty guards but my friend insisted and we got our answer. No.