That will take some effort. Since many sets use a Vokey 48 gap wedge, it will be uncommon. There a couple of “lost irons” internet shops in addition to eBay and other used club dealers. Most of the used club dealers only deal sets and not individuals. Besides switching to a Vokey if nothing turns up online, a new version T-100S 48 would not be radically different for just that one club in the set. Replacing a 7 iron would require more adjustment.
Your local pro shop or someone like Discount Dan’s (a pro shop that also sells online) can call Titleist to see if they can find a W head from the prior edition. Worth a try. A full set would be unlikely.

I would suggest EBay or 2ndswing if you really want another T100s. If you aren’t dead set, I would check out a 48* SM8.

I have one that came with my set, but has the Nippon Modus3 105 regular hard stepped once in it. Wish I wouldn’t have ordered it, wish I would have went the 44 bent to 45 and got a 50 vokey wedge. My old 50 vokey went 6 yards further than this 48 and it’s 2 degrees stronger with the same shaft. Expensive lesson….good luck!!