You can find iron shafts from golf component companies like GolfWorks. Titleist only sells assembled irons to ensure they are properly installed due to their warranty program. You can order driver and fairway club shafts from Titleist that will have the SureFit adapter installed or just look for used ones on eBay.

Shafts are available to be ordered through your local Titleist dealer. They come with the sure-fit adapters.

Shafts generally start at over $100, and the more exotic shafts can exceed $500. The fitting shafts can fit any Titleist driver from the 910 through GT. It might be more efficient to work with a fitter and narrow options down to 1-2 choices. You’ll likely be charged for the fitting, but will be cheaper than a couple of shafts that don’t work out well. Stores like 2nd Swing can offer a good selection of used shafts and they may come with a 30 day return policy.

You can order through your local retailer. You cannot "from what I know" order individual shafts through Titleist direct.

Side note: This can get expensive in a hurry if you're just trying them out. Even stock offerings are Over $100 for a replacement. I would recommend going to a fitting event and tell the fitter you're looking specifically to find the right shaft for your swing. They know what to do.