Since you discuss the Model 337, I assume you're after a 3" gun in .38Spl.
If you can live with a full stainless frame and cylinder, the .357Mag Model 60 has been offered with a 3" barrel and adjustable rear sight for several years now. They're fairly easy to find, both new and on the used market. A small number were sold this way in the early 90s in .38Spl form, before S&W started offering .357Mag J frames, but these guns are substantially less common than the .357Mag versions. FWIW 1996 and later J frames, .357Mag and otherwise, are about 1/10" longer overall than pre-1996 J frames that were sized for .38Spl only.
Around 1990, S&W offered a special edition Model 36 with bead blasted matte blue finish, a 3" barrel, and an adjustable rear sight. IIRC only ~1,000 were sold, but they seem to pop up on the used market more often than the low production number would suggest. Search for a Model 36-6.
The steel-frame Model 36 was offered for many years with two types of 3" barrels and a fixed rear sight. A tapered 3" barrel was offered on the M36 no-dash, although most of these guns were 2"; all M36-1s have a 3" heavy bull barrel. The latter seem slightly more common than the former.
Adjustable-sight Model 36s prior to the M36-6 are the proverbial needles in the haystack. They were only sold on a special-order basis; total production is estimated to be about 2,000 over the course of about 4 decades. [Edited to correct total.] Due to collector interest, these guns normally sell for whopping premiums over a standard fixed-sight gun.
If you've got your heart set on a lightweight frame, AFAIK your only option is the Model 337, but it did not sell very well and was not offered for very long. In addition to the 337Ti, S&W briefly offered basically the same gun as the 337PD with a matte black frame rather than the 337Ti's silver-colored frame, but I'm not sure if the 3" / adjustable sight gun came this way. All the 337PD photos that come up on the 'Net are 2" guns; I'll check my books later.
