I can appreciate the goal but its going to be tough to find all of those rods under one roof. I've been to a lot of fly shops, and don't think I've ever seen one that keeps a full stock of Loomis, Sage, Hardy, and Scott.
However... If the shop is confident you are going to purchase a high end rod, they may be able to hook you up and get everything there for you to try. I'm pretty confident If I told my local fly shop I was going to buy a $600+ rod and I wanted to try those 4 they'd do it. I'm a halfway decent customer though and have a history of dropping some coin there.
Which leads me to my next point which is off topic... Lots of guys buy rods, reels, and waders online because they can find them cheaper than at their local shop. It has been my experience that I can get high end items at my local shop for "online prices". Its kind of like being a good tipper when you're a regular at a bar...