As you say all things can be made, either by hand ( knife and fork we say ) or with tools. If you can get hold of the Yowl October 2018 . There is a nice piece on Graham Moag who makes Scott radiators. Gives an insight as to small volume honeycomb radiators are made. There are several companies remaking vintage radiators , and several who can supply ready built core banks. None are cheap so the alternatives are to purchase used ones ( with possible faults ) or to have a go yourself if the equipment is available. I have a very comprehensive workshop available , but if parts are made by specialists, most who make no real money, I buy from them. I have been an engineer for 65 years still working but I know my place!!!