On the other hand, I completely accept that. Welcome anyways!
eBay is a good source, or maybe someone on here has a spare set they took off when they upgraded pipes. Any 85-02 original set will do.
Since this is your first post even if it is not in the newbie intro form, Welcome to the Vulcan madness Robindea.
Great bike but search as I may I cant find anyone worldwide that supplies the original rear mufflers.
If I read your opening post correctly, you only need the the actual slip on mufflers from behind the exhaust crossover/power chamber. (aka the goat's belly or belly of the goat in Vulcan speak. lol
You may need new gaskets for the slip ons, but if the old ones do not leak, go ahead and use them.
thtanner is right, the pipes from any year vn700/750 from 1985 to 2006 will fit right up. (US models were 700 cc in 1985 only. All other models worldwide were always 750cc, and virtually all parts are interchangeable.)
History of the vn750 as we know it:
Here is a link to all the exhaust parts I found on Ebay just now by searching "vn 750 vulcan mufflers"
If you have the skills or know a mechanic who does, many Harley mufflers have been adapted to fit. Some of the members here can offer advice if you want to go this route.
Hope that helps you find what you need.