We can't find anyone to take his place by now.
take one's place
取代…人
你翻译的稍微有有问题,
we haven't found anyone who 【could】substitute for him
有一个could即解决了substitute时态问题,也代表一种语态,没有人能够代替他.
虚拟语态,表示与现在现实相反的意思.