As Michael said, there is a model BWV room on the BoardWalk. It's near Big River Grill.
That is about the only location which allows walk-in tours.
The Saratoga Springs Preview Center currently has replica model rooms of Animal Kingdom Villas and Aulani. Grand Floridian model will open there when sales begin. And they have access to a SSR room for touring purposes.
Tours of the model rooms at SSR are normally conducted by appointment only. They do not encourage members to stop by and wander. All guests must be escorted by a Cast Member. Whether or not they can accommodate you depends upon staff availability. If all of the on-duty sales Guides are with other customers (can easily happen), you will be asked to wait until someone is free. For that reason, it is highly recommended that you contact your Guide to set-up an appointment in advance.
A model room may be available at the Grand Floridian once it opens, but that remains to be seen.
You can certainly visit the resorts and look around public spaces. If you inquire at the front desk of a
DVC resort, they may be able to briefly show you a villa room. But that depends upon the availability of a clean, unoccupied villa AND a Cast Member who can leave the front desk to escort you to the room.