I lucked into a box of coins from a carboot sale to start with, I think that's where the old pennies and half-pennies came from. The three-pennies I bought specially, but they weren't very expensive. We also used modern 1p, 5p, and 10p coins (the later in small amounts), as well as gold (plastic) coins my wife had got from a LARP years before, and the random foreign coins — and yes, we live in Scotland, so it isn't hard.I never was able to run a game where all the money was real. It sounds like great fun. You must live where it is easier to get odd coins than I do. We get US and Canadian coins, and they often trade at par, regardless of the official exchange rate, but that is about it.
I felt that having physical money entirely changed the players (and characters) attitude to wealth.