Finding proper forks for older bikes

How difficult is it to spec and find a proper fork for an older road bike? I’m thinking about a bare frame (fairly sure mid-90’s road bike), but I’ve also checked into a few frames from the 50’s/60’s/70’s but the missing forks have always caused me to pass on them. I imagine I’d need to find the original specs on rake and trail, and then there would be the whole headset and bearing race fitment issues. I should probably just stick with finding complete bikes, but a 90’s Caloi has caught my eye recently .... (I should just pass on it....)