Given you've said it runs on a PP3, then a 1A supply is vast overkill. Almost any regulated (as opposed to unregulated) 9V supply will work fine. No, polarity is not standard. A cheapo Chinese one-adapter-fits-all supply with a selection of user-replacable plugs should suit you fine. Expect to pay around $10.
Since you mention the UK, the Hibaba
Hibaba Mains Universal Power Adaptor 1.5, 3, 4.5, 6: Amazon.co.uk: Electronics & Photo would seem to fit the bill, at 7 quid. As would Ex-Pro, and several other brands I've never heard of. Buy one, and if it doesn't work for you, buy another one but don't tell anyone.