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Europe or the uk are far better hunting grounds than Ireland, regular flea markets and dedicated fairs, but beware the avalanches of faked and reproduction items.
Suggest you join a FB group or dedicated online militaria forum and they should put you right on genuine vs dodgy and guideline prices. Most collectors are happy to point a newcomer in the right direction. Research average prices items fetch at auctions.
I would be wary of general antique dealers and auction houses here unless you are versed about what you want to buy. More often than not they don't have a clue and many things tend to be overpriced.
Treasure hunting, I dunno about digging around old and potentially unstable explosives. Sounds like a good way to lose an extremity.