So this JUST happened to me actually where I had a mill custom mixing for me and then they shut down. So my feed right now is corn. Which isn't ideal, but since these are breeding sows, I'm not worried about it until I get them breed/I'm feeding the next litter for butcher.

However, you're going to be massively constrained by what is available to you locally. Or at least you should be because if you're shipping shit around the country just to custom feed your hogs, that's incredibly contrary to permaculture. 

You need to set boundaries of your own and then prioritize them and then go from there. Start with cost, then consider gmo or no, organic or no, soy or no, corn or no. Then you basically just start looking around within whatever range you set. If you have a peanut processing facility near you, they've got good waste. Brewers/distillers is good too, protein is gunna be your biggest limiter. Then you're really just looking for other good stuff that you can get cheap. Eg if you have a dairy nearby, you can feed pigs 100% on their "waste" and hay. We've got black walnut processing in the region, so that waste would be prime. Food pantries have to throw out tons of perfect stuff.