Long time no see!
Calisthenics is pretty hardcore too, in a different way.
Fascia fitness (Iron Shirt Qigong/Neigong and I think Yin Yoga too) is a really good addition.
If you want to condition your shin bone, you can use a bamboo or wooden stick and rub up and down the shin, on the sides and at the front. I also use the steel brush and do a series of hits on the bone, it's more gentle than kicking the pole lol.
Making a steel brush is not that complicated to be honest, you don't have to build it with wood like me, a PVC handle can do (see below) or even just apply some epoxy at the base of the steel rods and then wrap the base with leather, electrical tape or those rubbery tennis handle tapes.
With PVC handle:
As for the rods, as mentioned, I used welding rods but you could also use clothe hangers. Don't use those flag poles, they are too thin. Each of the rods I use is about 37.40 cm long and 30.50 cm sticking out of the handle. About 1kg is a good weight too. The one you buy from shops are usually longer (50+ cm), they are heavier but softer as the length adds to flexibility of the rod.