The last version of the Amstrad CPC emulator CrocoDS v2.1 for the Nintendo DS went out in 2013 and is available on github. It is based on the WinCPC emulator by Ludovic Deplanque.

And now Kyuran has ported CrocoDS (RG350) on the portable console using OpenDingux (debian) : the Retro Game 350, which you can find easily on Amazon.

But a Sony PSP or PS Vita will let you emulate the Amstrad CPC better on a graphic point of view :

• Nintendo DS : 256 × 192
• RG 350 : 320x240
• Sony PSP : 480 × 272

You can see a vidéo by Oldschool is beautiful (french) which will show you how to use emulators on Sony PSP. To do the same thing on the PS Vita, you can check the site of Wololo.