Acceptable carbon steels for tamegashiri are within the 1060 - 1090 line. Anything above 1090 will be too hard, therefore too brittle, for use by someone who has not %110 perfected their technique. Anything below 1060 will be too soft, too forgiving, and will bend quite easily. 1060 spring is probably your best bet. It can handle occasional omote along with your backyard targets like pool noodles or water bottles, without much fear of losing shape or snapping on "kinda good" cuts. Once you get better with your cuts you can upgrade the carbon content in your sword. Contrary to popular belief, you can find well made, reasonably priced shinken at https://www.chenessinc.com I own the 3rd generation Mokko and have not had one single problem with the performance of the steel.