Thanks Pedalo, 5x red and 5x black 30amp for £6.35 from eBay as suggested.
eBay-based sellers often come-up cheaper than other web-based retailers, but that's not always true. That's why I use Google-Shopping to search for near-real-time online product sales, e.g.:
anderson plugs - Google Product Search
The other major advantage of using Google-search to start a quest for the most competitive price, is that it will correct spelling mistakes, it will match singular and plural words (e.g. "plugs" versus "plug") and it will also convert between words like "plug" and "connector".
Lastly, many online shops charge extortionate postage fees for even the smallest items (like 3-4 GBP for tiny parcels), so it's worth reading the small print.