Shin splits can be a big pain to deal with (literally) and really deter your training. Unfortunately, they are one of the more common running injuries out there, but that also means that there are many people who are looking for answers on how to heal them quick and keep them from returning!
For the best shoe options to help combat shin splints, make sure you check out our article here! These give you a list of shoes that have an ample amount of support and cushioning, and if you want one that offers support but is still light weight and won't weigh you down during your marathon, I would go with the Merrell Vapor Glove 2's, the Mizuno Wave Inspire's, or the Brooks Glycerin 14's. Finding a shoe that has enough support to stabilize your aching injuries but also is not too heavy can sometimes be tough, and these are three great options to go seek out, try on, and see how they feel on your feet.
As far as helping ease the pain of your shin splints and speed up the recovery process, the first place to start is with the good old fashioned RICE method: rest, ice, compression, elevation. I know you probably do not want to hear it, but you probably need to take a week or two (or more, depending on how serious the shin splints are) completely off of running and high-impact exercises. Your muscles need time to heal and repair themselves, and that's not going to happen if you continue pounding on them. Be sure to ice them for 20 minutes each day, and invest in a decent pair of compression socks that will help promote bloodflow to your shins. Finally, at the end of the day when you're just lounging around or preparing for bed, elevate your feet up above your heart for 20-30 minutes. If pain subsists throughout the day, take an over-the-counter muscle relaxant and pain reducer. And of course, always see your doctor for a professionals' opinion!
Good luck with your marathon training!