The Flavor Apprentice has a whole line of "DX" -- diketone free -- flavors, but also, Vanilla Swirl, which is a version of their Vanilla Custard with the diketones removed -- it's a good flavor, true vanilla, nicely sweet and creamy. Mixed with their DX Bavarian Cream, it will give a real custard flavor.
Capella has a line of "v2" flavors, though some of them aren't great -- I find their vanilla custard v2 just horridly artificial-tasting. Their "Sweet Cream" flavor is diketone-free, and very authentic-tasting.
FlavourArt, I think, has removed diketones from most of their flavors, and I think any that still remain are noted as such.
For TFA and Capella, bullcityvapor.com is a great resource; for FlavourArt, the only place I know for sure is ecigexpress.com; Wizard Labs may also carry them, but I'm not sure.
Andria