Final Option
Yes I very fortunate to find a sheath. I am lucky that I have many friends who collect Randall's. If one of us is in need of something particular, usually most of us will know what it is and are on the look out for the individual.
When you say that its "seems like common thing to separate the knife from the sheath", it is my opinion that the sheath get lost or more likely is so old they have fallen into disrepair or totally unusable.
At the Blade Show each year it is very common for people to walk around and ask about a particular Randall they have with them. They want to know price, age, etc. Frequently the sheath they have with the knife is incorrect.
I bought a early 50's Randall with not sheath, so I am the same boat as you. I feel I was lucky to find one old sheath, but finding two would be like winning the lottery.