My 2 (3 if you count Robinson Wheelworks) favorite LBS's wouldn't dream of making someone buy a bike before trying it just because the shop doesn't have their size in stock.

My LBS would order the size, and if I didn't want it they'd just sell it to someone else.

I've heard some people say their shop wanted a deposit (which would go toward whatever bike they eventually purchase) before ordering sizes.

The sizes you are looking at really aren't all that unusual, can you talk your LBS into ordering without making you purchase sight-unseen?

Where are you? There might be a TE'er near you who can recommend an LBS with reasonable ordering policies.