Hi Bon Hon,
Congrats! The ME series of Ingenieurs really seem to idealize what the Ingenieur series stands for.
I answered a similar question in this forum a while ago: Alternative strap for Ingenieur AMG Ceramic (2nd post).
The quick answer is to turn your Plastiki around and look at where the release pin that releases the strap is. If it's in the middle, then any strap with a release pin in the middle should fit the watch. Other release pins might be on the left side, so any strap with a release pin on the left side of it should fit.
I'm pretty sure the black rubber strap on the regular Mission Earth has the release pin in the middle, so if the blue strap on your Plastiki has the release pin in the middle then you can interchange the straps.
I don't know the reference numbers for the straps though.
Or just go to one of the boutiques or authorized dealers and go see if they will let you try on different straps! It's a great excuse to go make a visit.
Good luck!
Francis