The
Standard Catalog of Smith & Wesson by Supica & Nahas- the go-to guide for all things S&W- indicates that TBC3155-TBL7954 were made in 1987. (All standard commercially-sold S&W autoloading pistols were lumped into the same serial number range during this time period, so this range of numbers should NOT be used to deduce a Model 669-specific production total.)
BTW most people on these forums will replace the last couple of digits of their serial number with the letter "x" for privacy reasons (e.g. TCW85xx).
The Model 669 uses the same mags as all other 69-series pistols. In these market conditions, all bets are off when it comes to finding any.
However, based on a visit to a recent large gun show, I recommend sifting through the piles of used mags at the individual vendor tables, particularly the mags with no markings or unclear ones. I noticed many "mystery mags" for older pistols at these tables. Take the pistol if you can; if security requires you to zip-tie it at the door, ask them to tie it through the barrel so you can still test-fit mags.