Hi Mel,
one company i would feinately try is "Pro Impressions".
I saw them at Olympia earlier in the year and they have an extensive range of tips. I get the Pro Impressions Gold half cut out well tips. They are very strong with re-inforced sides and they are a lovely shape with a great curve which isn't too much.
They do lots of different airbrush tips too that can be used with Acrylic L&P, if you give them a ring you can order a brochure.
Phone no: 0116 2698444.
They will probably be at the Nail and Beauty show in Excel so check 'em out if you can, they did a geat promo at Olympia and i got 500 tips for £12.99. Great quality at great prices.