in what time frame did S & W stop selling guns to hardware stores and such and only sell to distributors?

They never did.

Most of the hardware co-ops such as True Value (True Serv), Ace Hardware, Paris-Dunlop, and others just got out of the gun business (at their headquarters). If you are asking if when they quit selling 2 or 3 guns to individual hardware stores if they just wanted to order a couple...probably sometime after 1968.

True Value got out of warehousing guns in their distribution centers in the 1990's. I have no idea on any of the others, but I believe that none of the hardware co-op headquarters/distribution centers have FFL's any more.

The other thing is, most hardware stores anymore don't have FFL's or sell guns- some that don't sell guns do sell ammunition.

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Lost it all in a boat accident

I was thinking along the lines of when somebody gets a letter on a S & W and it letters to some hardware store and it was delivered in 1935 or some some other year.

You will find that much more frequently the "Hardware company" the guns were shipped were companies like Salt Lake Hardware Co. in Salt Lake City, or Paxton & Gallagher in Omaha. These were distributors or wholesalers, not "hardware stores", they were the companies that supplied the hardware stores.

I think after the GCA [Gun Control Act] 1968 but I may be wrong.

I think Dick Rumbaugh may be right in referencing passage of the 1968 GCA. I can tell you with certainty that S&W (and Colt, Ruger and most other manufacturers) only sold directly to distributors (even if they required you to be a certified - insert brand name here - dealer), never directly to gun shops, in the early to mid-1970s, as I owned a gun shop back then, and would have dearly loved to be able to deal directly with the factory, instead of playing games with the distributors to get any decent (read saleable) guns! In fact, I had to use distributors throughout the U.S. in order to maintain a decent stock of S&W and Colt handguns. IIRC, Weatherby and Browning weres about the only manufacturers with which a gun shop could deal with directly, and Browning was a PITA. In fact, I threw the Browning rep out of my store after several unpleasant dealings with him (as well as their headquarters), and returned all my remaining Browning inventory. Roy Weatherby, on the other hand, was a true gentleman, and a friend, as well. He always bent over backwards to make sure everything could be done at his end to make things go well, even to the point of coming to my store (in Arizona) when we opened it to meet potential customers! Even after closing the store, he and I exchanged correspondence until he passed away. In any case, I digress, sorry. The switch to a strictly distributor based system may have coincided with the 1968 act, but was probably well along in the changeover process anyway, as it was, likely, becoming more and more inefficient for the factories to sell to thousands of small shops, with many small orders, by comparison to selling large orders to a (relatively) few large distributors. It also aided in streamlining production and forecasting production schedules for different models. A cost effective move for the manufacturer, not so great for the dealer.