Honestly, a Google search is probably your best friend here. With the way SEO works, typically the first page of results are fairly reputable companies, so I'd explore what comes up there.
I have tried Google searching but haven't found it easy to find many good suppliers. I've noticed there are quite a few paid directories. Would you recommend using any of them or would you stay clear?
It might be worth a small investment to see what's available. I'd reach out to the companies you're thinking of paying to determine whether they're worth your time to reach out to.
Just want to share my own experience as I start-up, it is very difficult to deal with most of the national brands. A lot of them do not even want to deal with drop shipment and payment terms with start-up. I end up using my credit card for all the stocking orders.
Not sure about the UK but check out AliBaba (They can connect you with companies from a lot of countries) or Wholesale Central. You guys should check out shopify's blog. They have some pretty good stuff there especially about product sourcing.
