What I remember:
- Published no later than 1990, probably more like 1985
- Near future setting, possibly featuring a vague Eastern/Western cold war scenario
- A boy of ~10 learns that he has a clone of the same age
- The clones secretly work together to ... do something that foils the plans of the adults who created them
- There may be a second book, where the boys learn there is a third clone
- The copy I read (US edition) was a slim hardcover of perhaps 150-200 pages
- Cover or dust jacket was primarily yellow
- Interior had some black-and-white illustrations, particularly on the end papers or near the title page
Any assistance locating this is appreciated!