You need to go to a higher end lighting store, who should be able to order most items out there. You can also find a local designer that will buy the items for you or you can go to some online vendors that will sell you these items.

Here is one I found. I've gotten a quote from them, but never purchased from them:
https://ladesignconcepts.com/

You can also try Maddie G Designs, who offers this service,

http://www.maddiegdesigns.com/

I haven't used her myself (I live in Canada so I have to factor in extra shipping and duty) but the idea is intriguing, and I wish I knew of a Canadian equivalent.

me too

Accessories are the most difficult