We do conscript capital to fund military spending, through taxation. It’s levied across the whole society according to ability to pay. There are always arguments about who should pay what, but thats what democratic politics is there to mediate.
Of course there is an argument that since individuals face conscription into the military, so why not conscript industry? But of course the US government had already laid down the legal basis for this by 1935 when this book was published. In fact they did so during WW2 in the form of commandeering, the power to compel any producer in the country to accept war orders, along with the imposition of price controls.