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For an Ergo Dox, you might be best to start with uniform profile keycaps, such as DSA. A few DSA sets have even been including Ergo Dox add-on kits recently. Most other sets are sculptured to fit a more conventional layout (e.g. ANSI) and you might not get all the keycaps you need to fit an Ergo Dox.
Although you can pay someone to mod a keyboard for you, most of the modifications are not that difficult as long as you take your time as you start, and don't get frustrated with boredom part way through. Gives a real sense of accomplishment too, knowing that you made each and every thing in the keyboard yourself!