I didn't realize this subforum existed. I placed this query in the HANDGUN HUNTING sub forum in error.

Please identify inside-the-waistband holsters made for S&W 640 DAO 357 Magnum revolvers with 2.125-inch barrels. I prefer holsters with belt loops rather than clips, and some method of securing revolver within holster - perhaps thumb snap?

These Bianchi holsters seem to meet your bill
55L, Black widow, or the 7 shadow II


Google can be your friend.

Many thanks for pointing me in the right direction. I think I know what I want, but I haven't found it.

Small of the back (behind the back) holsters have a severe angle for the revolver to allow convenient drawing of the weapon. Since the revolver's butt and grip are still readily available, this angle would be extremely convenient for me to use in a cross-draw holster when sitting. Does anyone offer such a cross-draw holster with an exaggerated angle?

I am a fan of Garrett Industries IWB and OWB holsters. Leather lined kydex and other options as well. I own 4 plus a couple of mag holders.

Very good people and product.

I've carried 649s and 642s for years in the Bianchi 55L, and have been quite happy with this set up. In Recent years I've used the Blackhawk Speed Classic and like it a lot, it holds close to the body and conceals better.

I bought an ETW tuckable holster. It does not have the features you are looking for--it has a clip and no retainer. I consider it a high quality product and ETW might make one that has your features. They supply a tube of treatment so that your gun will slide out easily. Even after treating, the fit is so good that the gun doesn't fall out when turned upside down and shook. I like the ability to tuck my shirt in and it doesn't show.
Having said that about holsters, Duluth Trading, the buck naked underwear and ballroom pants folks, makes a pair of firehose pants with a zipper pocket on the right front. These pants are called Foreman fire hose and listed on their site under casual pants. I find that wrapping my pistol in a handkerchief and dropping it into that pocket is very comfortable way to carry. BTW I like the pants, they come in coal, brown or khaki.

There's a Bucheimer on eBay at the moment.

I bought a Don Hume IWB holster with snaps. It should be delivered tomorrow. I'll try it for a couple of weeks. If it does what I want it to do, I'll report. If it does not, I'll report that, too. Then I'll resume the search.