The old school big lumps of copper soldering irons are plentiful on carboots, usually for peanuts. If anyone's into flint knapping they are a good source of mallet heads, or if you just want a copper mallet for general engineering, cheaper than getting a Thor, ok you'll have to shape it some but its easy to work.
atb
Tom
PS I cheat and use a old/spare electric soldering iron when I'm using pine resin glue. The one I use is the smallest/ least hot sort. You can get irons that run off car battery voltage, I picked one up NOS from a army stores. Just need to fit a cigarette lighter plug to the other end. I admit I didn't realise it wasn't mains voltage at the time, I thought I just needed to slap on a 3 pin plug. Good job I read the label before I did.
i sort of regret not picking up a unissued 1950s field soldering kit. I couldn't justify it but it was a lovely
thing, a tin box with irons, a brazier thing and all these solid fuel packs that fitted into the brazier to heat it for x number of minutes.
The tool guy on Haslinden Sunday carboot usually has unissued government issue irons on his stall, very cheap. I've ended up with three sizes for no good reason at all.