Welcome to the CP lover's website.
Not so much questions, just a few in fact.
The CP320 "Super Emeraude" shares a common 2 seater ancestor (the CP301A "Emeraude") with the CAP10 but it is not aerobatic. Its handling is similar but it's load factors are only +3.8G/-1.52G at a mass of 700 kg and +4.4G/-1.76G at a mass of 660 kg.
You can also sea on pictures that the rudder of the CAP10 is much larger than the one of the CP320 to make the recovering faster from spin.
The only two fully aerobatic Piel aircraft are :
1/ The CP750 "Béryl", as least as efficient as the CAP10 for aerobatics, but in tandem configuration...
2/ The CP1320 "Saphir"
This 2/3 seater is derived fron two former CP's
- The CP80 (single seater - F1 racer)
- The CP100 (prototype of the CAP10)
Even if this doesn't show off, the CP1320 shares the wing structure of the CAP10, and is fully aerobatic.
It's load factors are +6G/-3G at a mass of 700 kg and still +4.4G/-1.76G at a mass of 870 kg.
Most of amateur builders are not aerobatic pilot,
and they consider their CP1320 as a super CP320 (1 extra seat, faster, more payload, retractible undercarriage, etc...) but not as an aerobatic airplane, even if it is one.
But in a fixed undercarriage configuration (and without any fancy or heavy personal addings) with a lycoming IO-320 or IO-360, it would be as efficient as the CAP10 for aerobatics, in a side-by-side configuration... With a third seat or extra baggage payload for level flight as bonuses.
The plans of the the CP1320 are available both in french or in english...
But, if your dream is really to build a CAP10 and nothing else, you should know that a few CAP10B are amateur built. (like the F-PYPK ; in France the letters F-P*** are given to amateur built airplanes)
It should still be possible to buy the plans, but I don't know who sells them know.