I got curious about this, thinking about the old wooden rim bikes that used to be hanging in some older bike shops.

Apparently the 28" tubular size was the same as today's tubular rims size, though the profile may have been different. If any antique bike nuts want to chime in here, info is welcome!

Anyhow, it seems some people are using regular cyclocross tubular tires (700x34) on old wood rims with success.