Yes, you can get the insoles separately, they’re about 25quid-ish. They fit in Shimano shoes, but the shoes are narrower and they reduce the volume so they certainly won’t help with your toe box problem.
Specialized shoes have some tilt built into them. I’m not totally clear on this, but I think it’s the whole shoe which is tilted. You can add tilt to a shoe using wedges under the cleats.
I know the author recommends dealing with tibial varum (bow legs) by tilting the whole shoe and the differences in the forefoot with the wedges (as this is what he’s advised me to do). I’ve had to put a number of wedges under the cleats of my shoes, and then use one of the forefoot wedges under one foot.
You can see this makes a huge difference to the tracking of the knee just by looking down. This is a big difference and I really wish I’d discovered all this sooner before I caused damage. I haven’t measured my power output, but I’m feeling much stronger on the bike and I’m also able to maintain a higher hr longer. Very unscientific and I’ve had to spend ages off the bike for my knee to recover.
I’ve always worn the sides of cranks and chainstays and had numb feelings in my feet after long rides. All this was due to bad tracking of my knees. There is more to think about than just the angle of cleats which all the magazines mention.
I also know that the author of that report is experimenting with different insoles. He’s finding that some cycle specific insoles are not strong enough to support the foot arch and also the arch support is slightly too far forward, inferring with the effect of the forefoot wedge. I’m still experimenting with soles at the moment.