Forgefix. They are brilliant, especially for the price. They're passivated, so won't rust, countersunk, and they go in so smoothly I never soap them. Hardly bother with a pilot either, unless very near the end. I get them from Amazon, and look at the reviews. I'd say they are on a par with turbo gold, but less than half the price. Love them.
Decking screws or stainless steel would be a better choice.
what do you recommend, and where can I find it? TIA
They are made from carbon steel, so will definitely rust if used outside.
They have loads of screws on offer. EG GOLDSCREW PLUS PZ DOUBLE SELF-COUNTERSUNK WOODSCREWS 4.5 X 30MM 200 PACK for 86p Worth a look through the section on woodscrews