I did this most recently. Bought a letter on a gun I had hoped to purchase from a friend.
While buying his Ruger model 1 I mentioned I would like to buy the special Parker 20 gauge if he ever wanted to sell it.
A deal was made and I now own it.
I plan on doing an article for The Parker Pages once I have all of my research done.
I also bought the consecutive SN gun letter for a matching 16 gauge purchased by the same buyer.
The search is on for that Parker.

If there is very much money involved in the deal I always try to do the same.

I didn't have time to order a letter before the auction ended.