We get occasional requests for 27" rims or wheels. It wouldn't be hard for us to make 27" rims, but I don't think it's a good idea. Converting old 27" bikes to 700c is simple and almost always my preference.
A bit of background; 27" wheels were used mostly on American market mid and lower-range production bikes. There are some exceptions, but top-end frames with 27" wheels are relatively rare. The popularity of 27" wheels waned in the late '70s or early '80s when 700c became the near-universal road bike size. Today there are few choices of good quality 27" rims or tires and I don't know of a single new bike that still uses that size. The main reason to switch to 700c is to gain access to many more high quality tires and rims in more widths. 700c rims and tires are available in almost any bike shop anywhere in the world. You'll also gain a bit of extra tire or fender clearance.
|A 27" wheel hiding behind a 700c rim|
|Determining required brake reach|
I'm sure that there are some who will want to keep their bikes as original as possible. For a high-end production or custom frame that you view as more of a collectible than a user, this makes sense. Otherwise I would get a second set of 700c wheels for riding and keep the originals for display.