I don’t believe Titleist sells shafts direct, but I’ve had wonderful experiences with https://theshaftstore.com
The adapter and a grip is included in the purchase price for many shafts.

I have used them too and the service is fantastic.

You can also go to any Authorized Titleist Retailer and they can order a shaft direct from Titleist if that is what you prefer.

I have ordered a Titleist approved shaft through an authorized dealer before.

TS, TSi, TSR, fairway shafts are all interchangeable. Prices are pretty low on used TS fairways so it might be cheaper to buy a whole club with the shaft you want from a private seller or second hand golf shop. Then you have a spare head in case your old one cracks given its age.

Actually, any Titleist fairway shaft since the 913 series is interchangeable. Of course, likely only the shaft would be worth keeping from a 10-12 year old club. A new shaft could easily be more expensive than a complete used club even in the TS and TSi series,, as Dale indicated.

Any third party shaft provider can only use a third party adapter. Most work but Titleist does not cover hosel damage if it fails. Titleist only supplies factory original adapters on shafts sold by Titleist.