If you want one off the shelf I think you'd be best avoiding ones using the usual canola or sunflower oils as they can be inflammatory. Also, obviously, avoid added sugar!
It can be tricky to find commercial dressings made with good oils (olive oil or avocado oil for example) but if you have an immersion blender you can make a creamy mayonnaise at home. Search Keto mayonnaise on youtube for the method. It should keep a week in the fridge....I have totally been meaning to make some myself!
But the easiest option I find is just to shake up a vinaigrette in a jar using 2 - 3 parts good olive oil to one part vinegar or lemon juice plus some salt and (optional) mustard and/or fine chopped herbs.
Edited to add: I had a bit of a search and see there is a UK company called Hunter & Gather who look to be making high quality dressings. No doubt there are others too.
Some of the supermarket dressings that feature "olive oil" on the front label turn out to contain mostly rapeseed/canola, so it is a bit of a minefield out there!