Kind of a circular problem. In order to release a lot of fish you need a shitload of eggs. That requires a lot of adults. To get a lot of adults you need to not kill them in fisheries so you need to manage in-season or have good forecasts. You'll need a large hatchery with clean, cold water to produce the huge yearlings.

It can be done but would take money and commitment. And at the cost of the wild stock in those rivers. But, do you want a reasonable annual fishery or continuous closures??