Several years ago I bought inlay replacements cut from acoustic cloth from a chap selling these in eBay here in Germany. Should last essentially forever. The original foam ones should ship with a set of OEM replacement earpads. Those have always been kinda expensive, no clue what the quality of aftermarket options is like though. (If need be, people in the past have resorted to slicing such pads open from the back and restuffing them.)
The handband padding design kinda sucks, it's just too narrow. No wonder it flattens out in no time. At the very least consider upgrading to the HD650 part. I just taped a piece of foam in place, looks a bit ghetto but is way more comfy than stock. There may be fancier ways of going about it.