You'll find you're going to clock up quite a few miles looking for the right car. My search for a spitfire took me from Oxford to Nottingham, Portsmouth, Reigate, Bedford, London and finally bought my car from Portishead.
The Heralds are all 50+ years old & as with most cars of the time, they weren't exactly rustproofed, there will be quite a lot of basket cases out there. As there aren't very many up for sale at any given time you will need to be prepared to travel. The one I shared in my previous reply sounds like it's had a fair amount of money thrown at it. It's probably worth contacting the seller and asking if they would be willing to meet somewhere halfway (It's worth noting their ad was posted over a month ago, if they're keen to sell they might be obliging).