Just this week I bought a .458 SOCOM from a fella here on AR15.com and was fortunate that the deal included dies, 100 loaded rounds and 100 pieces of new Starline Brass so it was an instant set up for me. If you don't handload, I would tend to agree with you that the pickings are slim for ammo. If you don't, now would be a good time to explore that option. Like Bldsmith said there is a lot of good information over on the 458 SOCOM forum, but it is down at the moment.
I have been handloading for about 40 years now and still thoroughly enjoy the results of rolling my own. Most people do and the cost savings aren't bad either. With todays inflated prices and availability, it wouldn't take very long to recover your up front costs for getting set up. You can load single stage to learn and advance to an entry level progressive and then into a more complex machine if you really get into it. Handloading gives you a lot more options for almost any caliber you choose to load for, too. The costs are also a lot less, but how much you choose to spend on plinking, hunting and accuracy bullets are up to you. Some people like to play with loads, while others like to find a load they like and stick to it forever. Its easy and fun and can be a habit forming lifelong hobby.
So far, at least in TX, handloading components are readily available and if availability is good where you live, your new 458 won't sit idle and you will never have to rely on store bought ammo.