Click Plastics are my go to merchants in the UK. It might not look like they have a lot of stock by their website, but ring them up as they stock 75% more items than are listed online. If they don't have it they will do their best to acquire it, they go the extra mile which is why I use them. They ship UK wide for cheap prices which I've never had a problem with. Use them and you'll never need another builders merchants again!