Hercules hubs appear on Ebay all the time. But note that the correct wheels on this bike are 32 spokes front, 40 rear. The rims should be Dunlop 26 x 1 3/8. I didn't bother to count the spokes in your photos, but I'm willing to bet your Shimano hub has 36 spokes so you will need to replace the whole rear wheel.
The correct wheel will turn up, in time; put out a search for it, but don't put whole lot of effort into finding it. That will only increase the price, if you know what I mean.
The correct chain guards appear on ebay as well.
I just made my way to the man cave and the front wheel is 36 spokes with a Wald hub and, as you posited, the rear wheel has 36 spokes. So it's a 36/36 instead of the 32/40 as it would properly be. I'd like to have this ready for the 3-speed tour in May next year, but it's not a biggie if it isn't since I already have my Raleigh.
For now at least, I'll likely just keep the front wheel and put the Sturmey 3-speed wheel on it as I disassemble and clean the bike up.