Been to Hershey several times along with the smaller shows within a day drive of home. What I've seen isn't so much the manufactures bringing rigs in but the area dealers showing what they have on hand. I also toured Tiffin last summer and what you will see is what has recently come off the production line to fill orders. No guarantee the particular model you are looking for will be on the lot.
Research the shows and find the dealers who will have rigs on display and call them to find what models they will actually have available to walk thru.
Probably your best option is go thru the manufacture to research their dealer network to see who has the coach you are looking for available. This only applies to new rigs. Used, well you will just have to search.
Now the thread hijack question - how did a potential buyer find the rig they wanted before the internet?