Unfortunate about the root bark situation also ...
In case you will not get where you want, maybe try growing some mescaline cacti? I guess they are legal in most countries? Could be an interesting plant too I guess and definetly is regarded as a medicine too, which could suit your purpose.
As you only have 100 g bark left, also dont throw it away after an extraction and maybe try to boil it another time or maybe up to 3 times. Maybe you can get more actives out.
About smoking: Changa in my eyes is ineffective. When I load what is equivalent to 30 mg into a bong I just get a medium experience. Pretty similar to 10 mg of pure smoked. There will always be a huge amount left in the herbs after smoking and also a small amount is always burned due to local overheating. That's why for efficiency you should also only use the pure freebase powder, as you probably did so far.
The easiest way would be using an oil burner / oil pipe / meth pipe / crack pipe (it has many names) although this will also cause some combustion, but less than changa probably. But maybe you tried exactly this which led to a low efficiency. If you did another way, maybe try out the oil burner as a quick and easy alternative with like 10 mg portions and see if that is any better.