It might be an idea to get in contact with Philippe Lang ASAP. If he can't accommodate the the designs you want for your custom key caps then he should at least be able to get you the blanks required so that you can print your own transparent stickers or even use a professional company like WASD.
Kipper2k in cooperation with Amiga on the Lake has a project to create new keyboards using Cherry MX type switches and also create molds for the unique to Amiga keycaps. This will be more expensive than keycaps only (for existing Mitsumi hybrid switch Amiga keyboards) option from A1200.net
I have seen the web site that sells all kinds of stickers for keyboards. Another sold keyboards for specific software. Finding out exactly what the standard is for video keyboards is another step.